diff --git a/src/CharWidth.ts b/src/CharWidth.ts
index 90673b2b..2165d9ba 100644
--- a/src/CharWidth.ts
+++ b/src/CharWidth.ts
@@ -161,7 +161,7 @@ export const wcwidth = (function(opts: {nul: number, control: number}): (ucs: nu
       if (num < 127) {
         return 1;
       }
-      let t = table || init_table();
+      const t = table || init_table();
       if (num < 65536) {
         return t[num >> 4] >> ((num & 15) << 1) & 3;
       }
diff --git a/src/EscapeSequenceParser.test.ts b/src/EscapeSequenceParser.test.ts
index 2d85c466..d9ea64ce 100644
--- a/src/EscapeSequenceParser.test.ts
+++ b/src/EscapeSequenceParser.test.ts
@@ -9,7 +9,7 @@ import * as chai from 'chai';
 
 function r(a: number, b: number): string[] {
   let c = b - a;
-  let arr = new Array(c);
+  const arr = new Array(c);
   while (c--) {
     arr[c] = String.fromCharCode(--b);
   }
@@ -42,7 +42,7 @@ class TestEscapeSequenceParser extends EscapeSequenceParser {
 }
 
 // test object to collect parser actions and compare them with expected values
-let testTerminal: any = {
+const testTerminal: any = {
   calls: [],
   clear: function (): void {
     this.calls = [];
@@ -89,7 +89,7 @@ class DcsTest implements IDcsHandler {
   }
 }
 
-let states: number[] = [
+const states: number[] = [
   ParserState.GROUND,
   ParserState.ESCAPE,
   ParserState.ESCAPE_INTERMEDIATE,
@@ -108,7 +108,7 @@ let states: number[] = [
 let state: any;
 
 // parser with Uint8Array based transition table
-let parserUint = new TestEscapeSequenceParser(VT500_TRANSITION_TABLE);
+const parserUint = new TestEscapeSequenceParser(VT500_TRANSITION_TABLE);
 parserUint.setPrintHandler(testTerminal.print.bind(testTerminal));
 parserUint.setCsiHandlerFallback((collect: string, params: number[], flag: number) => {
   testTerminal.actionCSI(collect, params, String.fromCharCode(flag));
@@ -126,14 +126,14 @@ parserUint.setOscHandlerFallback((identifier: number, data: string) => {
 parserUint.setDcsHandlerFallback(new DcsTest());
 
 // array based transition table
-let VT500_TRANSITION_TABLE_ARRAY = new TransitionTable(VT500_TRANSITION_TABLE.table.length);
+const VT500_TRANSITION_TABLE_ARRAY = new TransitionTable(VT500_TRANSITION_TABLE.table.length);
 VT500_TRANSITION_TABLE_ARRAY.table = new Array(VT500_TRANSITION_TABLE.table.length);
 for (let i = 0; i < VT500_TRANSITION_TABLE.table.length; ++i) {
   VT500_TRANSITION_TABLE_ARRAY.table[i] = VT500_TRANSITION_TABLE.table[i];
 }
 
 // parser with array based transition table
-let parserArray = new TestEscapeSequenceParser(VT500_TRANSITION_TABLE_ARRAY);
+const parserArray = new TestEscapeSequenceParser(VT500_TRANSITION_TABLE_ARRAY);
 parserArray.setPrintHandler(testTerminal.print.bind(testTerminal));
 parserArray.setCsiHandlerFallback((collect: string, params: number[], flag: number) => {
   testTerminal.actionCSI(collect, params, String.fromCharCode(flag));
@@ -172,7 +172,7 @@ describe('EscapeSequenceParser', function (): void {
         chai.expect(p.transitions).equal(VT500_TRANSITION_TABLE);
         p = new EscapeSequenceParser(VT500_TRANSITION_TABLE);
         chai.expect(p.transitions).equal(VT500_TRANSITION_TABLE);
-        let tansitions: TransitionTable = new TransitionTable(10);
+        const tansitions: TransitionTable = new TransitionTable(10);
         p = new EscapeSequenceParser(tansitions);
         chai.expect(p.transitions).equal(tansitions);
       });
@@ -205,7 +205,7 @@ describe('EscapeSequenceParser', function (): void {
       it('state GROUND execute action', function (): void {
         parser.reset();
         testTerminal.clear();
-        let exes = r(0x00, 0x18);
+        const exes = r(0x00, 0x18);
         exes.concat(['\x19']);
         exes.concat(r(0x1c, 0x20));
         for (let i = 0; i < exes.length; ++i) {
@@ -220,7 +220,7 @@ describe('EscapeSequenceParser', function (): void {
       it('state GROUND print action', function (): void {
         parser.reset();
         testTerminal.clear();
-        let printables = r(0x20, 0x7f); // NOTE: DEL excluded
+        const printables = r(0x20, 0x7f); // NOTE: DEL excluded
         for (let i = 0; i < printables.length; ++i) {
           parser.currentState = ParserState.GROUND;
           parser.parse(printables[i]);
@@ -231,13 +231,13 @@ describe('EscapeSequenceParser', function (): void {
         }
       });
       it('trans ANYWHERE --> GROUND with actions', function (): void {
-        let exes = [
+        const exes = [
           '\x18', '\x1a',
           '\x80', '\x81', '\x82', '\x83', '\x84', '\x85', '\x86', '\x87', '\x88',
           '\x89', '\x8a', '\x8b', '\x8c', '\x8d', '\x8e', '\x8f',
           '\x91', '\x92', '\x93', '\x94', '\x95', '\x96', '\x97', '\x99', '\x9a'
         ];
-        let exceptions = {
+        const exceptions = {
           8: { '\x18': [], '\x1a': [] } // simply abort osc state
         };
         parser.reset();
@@ -276,7 +276,7 @@ describe('EscapeSequenceParser', function (): void {
       it('state ESCAPE execute rules', function (): void {
         parser.reset();
         testTerminal.clear();
-        let exes = r(0x00, 0x18);
+        const exes = r(0x00, 0x18);
         exes.concat(['\x19']);
         exes.concat(r(0x1c, 0x20));
         for (let i = 0; i < exes.length; ++i) {
@@ -301,7 +301,7 @@ describe('EscapeSequenceParser', function (): void {
       it('trans ESCAPE --> GROUND with ecs_dispatch action', function (): void {
         parser.reset();
         testTerminal.clear();
-        let dispatches = r(0x30, 0x50);
+        const dispatches = r(0x30, 0x50);
         dispatches.concat(r(0x51, 0x58));
         dispatches.concat(['\x59', '\x5a', '\x5c']);
         dispatches.concat(r(0x60, 0x7f));
@@ -316,7 +316,7 @@ describe('EscapeSequenceParser', function (): void {
       });
       it('trans ESCAPE --> ESCAPE_INTERMEDIATE with collect action', function (): void {
         parser.reset();
-        let collect = r(0x20, 0x30);
+        const collect = r(0x20, 0x30);
         for (let i = 0; i < collect.length; ++i) {
           parser.currentState = ParserState.ESCAPE;
           parser.parse(collect[i]);
@@ -328,7 +328,7 @@ describe('EscapeSequenceParser', function (): void {
       it('state ESCAPE_INTERMEDIATE execute rules', function (): void {
         parser.reset();
         testTerminal.clear();
-        let exes = r(0x00, 0x18);
+        const exes = r(0x00, 0x18);
         exes.concat(['\x19']);
         exes.concat(r(0x1c, 0x20));
         for (let i = 0; i < exes.length; ++i) {
@@ -352,7 +352,7 @@ describe('EscapeSequenceParser', function (): void {
       });
       it('state ESCAPE_INTERMEDIATE collect action', function (): void {
         parser.reset();
-        let collect = r(0x20, 0x30);
+        const collect = r(0x20, 0x30);
         for (let i = 0; i < collect.length; ++i) {
           parser.currentState = ParserState.ESCAPE_INTERMEDIATE;
           parser.parse(collect[i]);
@@ -364,7 +364,7 @@ describe('EscapeSequenceParser', function (): void {
       it('trans ESCAPE_INTERMEDIATE --> GROUND with esc_dispatch action', function (): void {
         parser.reset();
         testTerminal.clear();
-        let collect = r(0x30, 0x7f);
+        const collect = r(0x30, 0x7f);
         for (let i = 0; i < collect.length; ++i) {
           parser.currentState = ParserState.ESCAPE_INTERMEDIATE;
           parser.parse(collect[i]);
@@ -404,7 +404,7 @@ describe('EscapeSequenceParser', function (): void {
       it('state CSI_ENTRY execute rules', function (): void {
         parser.reset();
         testTerminal.clear();
-        let exes = r(0x00, 0x18);
+        const exes = r(0x00, 0x18);
         exes.concat(['\x19']);
         exes.concat(r(0x1c, 0x20));
         for (let i = 0; i < exes.length; ++i) {
@@ -428,7 +428,7 @@ describe('EscapeSequenceParser', function (): void {
       });
       it('trans CSI_ENTRY --> GROUND with csi_dispatch action', function (): void {
         parser.reset();
-        let dispatches = r(0x40, 0x7f);
+        const dispatches = r(0x40, 0x7f);
         for (let i = 0; i < dispatches.length; ++i) {
           parser.currentState = ParserState.CSI_ENTRY;
           parser.parse(dispatches[i]);
@@ -440,8 +440,8 @@ describe('EscapeSequenceParser', function (): void {
       });
       it('trans CSI_ENTRY --> CSI_PARAM with param/collect actions', function (): void {
         parser.reset();
-        let params = ['\x30', '\x31', '\x32', '\x33', '\x34', '\x35', '\x36', '\x37', '\x38', '\x39'];
-        let collect = ['\x3c', '\x3d', '\x3e', '\x3f'];
+        const params = ['\x30', '\x31', '\x32', '\x33', '\x34', '\x35', '\x36', '\x37', '\x38', '\x39'];
+        const collect = ['\x3c', '\x3d', '\x3e', '\x3f'];
         for (let i = 0; i < params.length; ++i) {
           parser.currentState = ParserState.CSI_ENTRY;
           parser.parse(params[i]);
@@ -465,7 +465,7 @@ describe('EscapeSequenceParser', function (): void {
       it('state CSI_PARAM execute rules', function (): void {
         parser.reset();
         testTerminal.clear();
-        let exes = r(0x00, 0x18);
+        const exes = r(0x00, 0x18);
         exes.concat(['\x19']);
         exes.concat(r(0x1c, 0x20));
         for (let i = 0; i < exes.length; ++i) {
@@ -479,7 +479,7 @@ describe('EscapeSequenceParser', function (): void {
       });
       it('state CSI_PARAM param action', function (): void {
         parser.reset();
-        let params = ['\x30', '\x31', '\x32', '\x33', '\x34', '\x35', '\x36', '\x37', '\x38', '\x39'];
+        const params = ['\x30', '\x31', '\x32', '\x33', '\x34', '\x35', '\x36', '\x37', '\x38', '\x39'];
         for (let i = 0; i < params.length; ++i) {
           parser.currentState = ParserState.CSI_PARAM;
           parser.parse(params[i]);
@@ -505,7 +505,7 @@ describe('EscapeSequenceParser', function (): void {
       });
       it('trans CSI_PARAM --> GROUND with csi_dispatch action', function (): void {
         parser.reset();
-        let dispatches = r(0x40, 0x7f);
+        const dispatches = r(0x40, 0x7f);
         for (let i = 0; i < dispatches.length; ++i) {
           parser.currentState = ParserState.CSI_PARAM;
           parser.params = [0, 1];
@@ -518,7 +518,7 @@ describe('EscapeSequenceParser', function (): void {
       });
       it('trans CSI_ENTRY --> CSI_INTERMEDIATE with collect action', function (): void {
         parser.reset();
-        let collect = r(0x20, 0x30);
+        const collect = r(0x20, 0x30);
         for (let i = 0; i < collect.length; ++i) {
           parser.currentState = ParserState.CSI_ENTRY;
           parser.parse(collect[i]);
@@ -529,7 +529,7 @@ describe('EscapeSequenceParser', function (): void {
       });
       it('trans CSI_PARAM --> CSI_INTERMEDIATE with collect action', function (): void {
         parser.reset();
-        let collect = r(0x20, 0x30);
+        const collect = r(0x20, 0x30);
         for (let i = 0; i < collect.length; ++i) {
           parser.currentState = ParserState.CSI_PARAM;
           parser.parse(collect[i]);
@@ -541,7 +541,7 @@ describe('EscapeSequenceParser', function (): void {
       it('state CSI_INTERMEDIATE execute rules', function (): void {
         parser.reset();
         testTerminal.clear();
-        let exes = r(0x00, 0x18);
+        const exes = r(0x00, 0x18);
         exes.concat(['\x19']);
         exes.concat(r(0x1c, 0x20));
         for (let i = 0; i < exes.length; ++i) {
@@ -555,7 +555,7 @@ describe('EscapeSequenceParser', function (): void {
       });
       it('state CSI_INTERMEDIATE collect', function (): void {
         parser.reset();
-        let collect = r(0x20, 0x30);
+        const collect = r(0x20, 0x30);
         for (let i = 0; i < collect.length; ++i) {
           parser.currentState = ParserState.CSI_INTERMEDIATE;
           parser.parse(collect[i]);
@@ -576,7 +576,7 @@ describe('EscapeSequenceParser', function (): void {
       });
       it('trans CSI_INTERMEDIATE --> GROUND with csi_dispatch action', function (): void {
         parser.reset();
-        let dispatches = r(0x40, 0x7f);
+        const dispatches = r(0x40, 0x7f);
         for (let i = 0; i < dispatches.length; ++i) {
           parser.currentState = ParserState.CSI_INTERMEDIATE;
           parser.params = [0, 1];
@@ -596,7 +596,7 @@ describe('EscapeSequenceParser', function (): void {
       });
       it('trans CSI_PARAM --> CSI_IGNORE', function (): void {
         parser.reset();
-        let chars = ['\x3a', '\x3c', '\x3d', '\x3e', '\x3f'];
+        const chars = ['\x3a', '\x3c', '\x3d', '\x3e', '\x3f'];
         for (let i = 0; i < chars.length; ++i) {
           parser.currentState = ParserState.CSI_PARAM;
           parser.parse('\x3b' + chars[i]);
@@ -607,7 +607,7 @@ describe('EscapeSequenceParser', function (): void {
       });
       it('trans CSI_INTERMEDIATE --> CSI_IGNORE', function (): void {
         parser.reset();
-        let chars = r(0x30, 0x40);
+        const chars = r(0x30, 0x40);
         for (let i = 0; i < chars.length; ++i) {
           parser.currentState = ParserState.CSI_INTERMEDIATE;
           parser.parse(chars[i]);
@@ -619,7 +619,7 @@ describe('EscapeSequenceParser', function (): void {
       it('state CSI_IGNORE execute rules', function (): void {
         parser.reset();
         testTerminal.clear();
-        let exes = r(0x00, 0x18);
+        const exes = r(0x00, 0x18);
         exes.concat(['\x19']);
         exes.concat(r(0x1c, 0x20));
         for (let i = 0; i < exes.length; ++i) {
@@ -634,7 +634,7 @@ describe('EscapeSequenceParser', function (): void {
       it('state CSI_IGNORE ignore', function (): void {
         parser.reset();
         testTerminal.clear();
-        let ignored = r(0x20, 0x40);
+        const ignored = r(0x20, 0x40);
         ignored.concat(['\x7f']);
         for (let i = 0; i < ignored.length; ++i) {
           parser.currentState = ParserState.CSI_IGNORE;
@@ -647,7 +647,7 @@ describe('EscapeSequenceParser', function (): void {
       });
       it('trans CSI_IGNORE --> GROUND', function (): void {
         parser.reset();
-        let dispatches = r(0x40, 0x7f);
+        const dispatches = r(0x40, 0x7f);
         for (let i = 0; i < dispatches.length; ++i) {
           parser.currentState = ParserState.CSI_IGNORE;
           parser.params = [0, 1];
@@ -680,7 +680,7 @@ describe('EscapeSequenceParser', function (): void {
       });
       it('state SOS_PM_APC_STRING ignore rules', function (): void {
         parser.reset();
-        let ignored = r(0x00, 0x18);
+        const ignored = r(0x00, 0x18);
         ignored.concat(['\x19']);
         ignored.concat(r(0x1c, 0x20));
         ignored.concat(r(0x20, 0x80));
@@ -707,7 +707,7 @@ describe('EscapeSequenceParser', function (): void {
       });
       it('state OSC_STRING ignore rules', function (): void {
         parser.reset();
-        let ignored = [
+        const ignored = [
           '\x00', '\x01', '\x02', '\x03', '\x04', '\x05', '\x06', /*'\x07',*/ '\x08',
           '\x09', '\x0a', '\x0b', '\x0c', '\x0d', '\x0e', '\x0f', '\x10', '\x11',
           '\x12', '\x13', '\x14', '\x15', '\x16', '\x17', '\x19', '\x1c', '\x1d', '\x1e', '\x1f'];
@@ -721,7 +721,7 @@ describe('EscapeSequenceParser', function (): void {
       });
       it('state OSC_STRING put action', function (): void {
         parser.reset();
-        let puts = r(0x20, 0x80);
+        const puts = r(0x20, 0x80);
         for (let i = 0; i < puts.length; ++i) {
           parser.currentState = ParserState.OSC_STRING;
           parser.parse(puts[i]);
@@ -746,7 +746,7 @@ describe('EscapeSequenceParser', function (): void {
       });
       it('state DCS_ENTRY ignore rules', function (): void {
         parser.reset();
-        let ignored = [
+        const ignored = [
           '\x00', '\x01', '\x02', '\x03', '\x04', '\x05', '\x06', '\x07', '\x08',
           '\x09', '\x0a', '\x0b', '\x0c', '\x0d', '\x0e', '\x0f', '\x10', '\x11',
           '\x12', '\x13', '\x14', '\x15', '\x16', '\x17', '\x19', '\x1c', '\x1d', '\x1e', '\x1f', '\x7f'];
@@ -759,8 +759,8 @@ describe('EscapeSequenceParser', function (): void {
       });
       it('state DCS_ENTRY --> DCS_PARAM with param/collect actions', function (): void {
         parser.reset();
-        let params = ['\x30', '\x31', '\x32', '\x33', '\x34', '\x35', '\x36', '\x37', '\x38', '\x39'];
-        let collect = ['\x3c', '\x3d', '\x3e', '\x3f'];
+        const params = ['\x30', '\x31', '\x32', '\x33', '\x34', '\x35', '\x36', '\x37', '\x38', '\x39'];
+        const collect = ['\x3c', '\x3d', '\x3e', '\x3f'];
         for (let i = 0; i < params.length; ++i) {
           parser.currentState = ParserState.DCS_ENTRY;
           parser.parse(params[i]);
@@ -783,7 +783,7 @@ describe('EscapeSequenceParser', function (): void {
       });
       it('state DCS_PARAM ignore rules', function (): void {
         parser.reset();
-        let ignored = [
+        const ignored = [
           '\x00', '\x01', '\x02', '\x03', '\x04', '\x05', '\x06', '\x07', '\x08',
           '\x09', '\x0a', '\x0b', '\x0c', '\x0d', '\x0e', '\x0f', '\x10', '\x11',
           '\x12', '\x13', '\x14', '\x15', '\x16', '\x17', '\x19', '\x1c', '\x1d', '\x1e', '\x1f', '\x7f'];
@@ -796,7 +796,7 @@ describe('EscapeSequenceParser', function (): void {
       });
       it('state DCS_PARAM param action', function (): void {
         parser.reset();
-        let params = ['\x30', '\x31', '\x32', '\x33', '\x34', '\x35', '\x36', '\x37', '\x38', '\x39'];
+        const params = ['\x30', '\x31', '\x32', '\x33', '\x34', '\x35', '\x36', '\x37', '\x38', '\x39'];
         for (let i = 0; i < params.length; ++i) {
           parser.currentState = ParserState.DCS_PARAM;
           parser.parse(params[i]);
@@ -819,7 +819,7 @@ describe('EscapeSequenceParser', function (): void {
       });
       it('trans DCS_PARAM --> DCS_IGNORE', function (): void {
         parser.reset();
-        let chars = ['\x3a', '\x3c', '\x3d', '\x3e', '\x3f'];
+        const chars = ['\x3a', '\x3c', '\x3d', '\x3e', '\x3f'];
         for (let i = 0; i < chars.length; ++i) {
           parser.currentState = ParserState.DCS_PARAM;
           parser.parse('\x3b' + chars[i]);
@@ -830,7 +830,7 @@ describe('EscapeSequenceParser', function (): void {
       });
       it('trans DCS_INTERMEDIATE --> DCS_IGNORE', function (): void {
         parser.reset();
-        let chars = r(0x30, 0x40);
+        const chars = r(0x30, 0x40);
         for (let i = 0; i < chars.length; ++i) {
           parser.currentState = ParserState.DCS_INTERMEDIATE;
           parser.parse(chars[i]);
@@ -840,7 +840,7 @@ describe('EscapeSequenceParser', function (): void {
       });
       it('state DCS_IGNORE ignore rules', function (): void {
         parser.reset();
-        let ignored = [
+        const ignored = [
           '\x00', '\x01', '\x02', '\x03', '\x04', '\x05', '\x06', '\x07', '\x08',
           '\x09', '\x0a', '\x0b', '\x0c', '\x0d', '\x0e', '\x0f', '\x10', '\x11',
           '\x12', '\x13', '\x14', '\x15', '\x16', '\x17', '\x19', '\x1c', '\x1d', '\x1e', '\x1f', '\x7f'];
@@ -854,7 +854,7 @@ describe('EscapeSequenceParser', function (): void {
       });
       it('trans DCS_ENTRY --> DCS_INTERMEDIATE with collect action', function (): void {
         parser.reset();
-        let collect = r(0x20, 0x30);
+        const collect = r(0x20, 0x30);
         for (let i = 0; i < collect.length; ++i) {
           parser.currentState = ParserState.DCS_ENTRY;
           parser.parse(collect[i]);
@@ -865,7 +865,7 @@ describe('EscapeSequenceParser', function (): void {
       });
       it('trans DCS_PARAM --> DCS_INTERMEDIATE with collect action', function (): void {
         parser.reset();
-        let collect = r(0x20, 0x30);
+        const collect = r(0x20, 0x30);
         for (let i = 0; i < collect.length; ++i) {
           parser.currentState = ParserState.DCS_PARAM;
           parser.parse(collect[i]);
@@ -876,7 +876,7 @@ describe('EscapeSequenceParser', function (): void {
       });
       it('state DCS_INTERMEDIATE ignore rules', function (): void {
         parser.reset();
-        let ignored = [
+        const ignored = [
           '\x00', '\x01', '\x02', '\x03', '\x04', '\x05', '\x06', '\x07', '\x08',
           '\x09', '\x0a', '\x0b', '\x0c', '\x0d', '\x0e', '\x0f', '\x10', '\x11',
           '\x12', '\x13', '\x14', '\x15', '\x16', '\x17', '\x19', '\x1c', '\x1d', '\x1e', '\x1f', '\x7f'];
@@ -889,7 +889,7 @@ describe('EscapeSequenceParser', function (): void {
       });
       it('state DCS_INTERMEDIATE collect action', function (): void {
         parser.reset();
-        let collect = r(0x20, 0x30);
+        const collect = r(0x20, 0x30);
         for (let i = 0; i < collect.length; ++i) {
           parser.currentState = ParserState.DCS_INTERMEDIATE;
           parser.parse(collect[i]);
@@ -900,7 +900,7 @@ describe('EscapeSequenceParser', function (): void {
       });
       it('trans DCS_INTERMEDIATE --> DCS_IGNORE', function (): void {
         parser.reset();
-        let chars = r(0x30, 0x40);
+        const chars = r(0x30, 0x40);
         for (let i = 0; i < chars.length; ++i) {
           parser.currentState = ParserState.DCS_INTERMEDIATE;
           parser.parse('\x20' + chars[i]);
@@ -912,7 +912,7 @@ describe('EscapeSequenceParser', function (): void {
       it('trans DCS_ENTRY --> DCS_PASSTHROUGH with hook', function (): void {
         parser.reset();
         testTerminal.clear();
-        let collect = r(0x40, 0x7f);
+        const collect = r(0x40, 0x7f);
         for (let i = 0; i < collect.length; ++i) {
           parser.currentState = ParserState.DCS_ENTRY;
           parser.parse(collect[i]);
@@ -925,7 +925,7 @@ describe('EscapeSequenceParser', function (): void {
       it('trans DCS_PARAM --> DCS_PASSTHROUGH with hook', function (): void {
         parser.reset();
         testTerminal.clear();
-        let collect = r(0x40, 0x7f);
+        const collect = r(0x40, 0x7f);
         for (let i = 0; i < collect.length; ++i) {
           parser.currentState = ParserState.DCS_PARAM;
           parser.parse(collect[i]);
@@ -938,7 +938,7 @@ describe('EscapeSequenceParser', function (): void {
       it('trans DCS_INTERMEDIATE --> DCS_PASSTHROUGH with hook', function (): void {
         parser.reset();
         testTerminal.clear();
-        let collect = r(0x40, 0x7f);
+        const collect = r(0x40, 0x7f);
         for (let i = 0; i < collect.length; ++i) {
           parser.currentState = ParserState.DCS_INTERMEDIATE;
           parser.parse(collect[i]);
@@ -951,7 +951,7 @@ describe('EscapeSequenceParser', function (): void {
       it('state DCS_PASSTHROUGH put action', function (): void {
         parser.reset();
         testTerminal.clear();
-        let puts = r(0x00, 0x18);
+        const puts = r(0x00, 0x18);
         puts.concat(['\x19']);
         puts.concat(r(0x1c, 0x20));
         puts.concat(r(0x20, 0x7f));
diff --git a/src/EscapeSequenceParser.ts b/src/EscapeSequenceParser.ts
index dea87f8d..71a06138 100644
--- a/src/EscapeSequenceParser.ts
+++ b/src/EscapeSequenceParser.ts
@@ -12,7 +12,7 @@ import { ParserState, ParserAction, IParsingState, IDcsHandler, IEscapeSequenceP
  */
 function r(low: number, high: number): number[] {
   let c = high - low;
-  let arr = new Array(c);
+  const arr = new Array(c);
   while (c--) {
     arr[c] = --high;
   }
@@ -62,8 +62,8 @@ export class TransitionTable {
 /**
  * Default definitions for the VT500_TRANSITION_TABLE.
  */
-let PRINTABLES = r(0x20, 0x7f);
-let EXECUTABLES = r(0x00, 0x18);
+const PRINTABLES = r(0x20, 0x7f);
+const EXECUTABLES = r(0x00, 0x18);
 EXECUTABLES.push(0x19);
 EXECUTABLES.concat(r(0x1c, 0x20));
 const DEFAULT_TRANSITION = ParserAction.ERROR << 4 | ParserState.GROUND;
@@ -73,9 +73,9 @@ const DEFAULT_TRANSITION = ParserAction.ERROR << 4 | ParserState.GROUND;
  * Taken from https://vt100.net/emu/dec_ansi_parser.
  */
 export const VT500_TRANSITION_TABLE = (function (): TransitionTable {
-  let table: TransitionTable = new TransitionTable(4095);
+  const table: TransitionTable = new TransitionTable(4095);
 
-  let states: number[] = r(ParserState.GROUND, ParserState.DCS_PASSTHROUGH + 1);
+  const states: number[] = r(ParserState.GROUND, ParserState.DCS_PASSTHROUGH + 1);
   let state: any;
 
   // table with default transition [any] --> DEFAULT_TRANSITION
@@ -421,7 +421,7 @@ export class EscapeSequenceParser implements IEscapeSequenceParser {
           }
           // if we end up here a real error happened
           if (error) {
-            let inject: IParsingState = this._errorHandler(
+            const inject: IParsingState = this._errorHandler(
               {
                 position: i,
                 code,
@@ -499,15 +499,15 @@ export class EscapeSequenceParser implements IEscapeSequenceParser {
           if (osc && code !== 0x18 && code !== 0x1a) {
             // NOTE: OSC subparsing is not part of the original parser
             // we do basic identifier parsing here to offer a jump table for OSC as well
-            let idx = osc.indexOf(';');
+            const idx = osc.indexOf(';');
             if (idx === -1) {
               this._oscHandlerFb(-1, osc);  // this is an error (malformed OSC)
             } else {
               // Note: NaN is not handled here
               // either catch it with the fallback handler
               // or with an explicit NaN OSC handler
-              let identifier = parseInt(osc.substring(0, idx));
-              let content = osc.substring(idx + 1);
+              const identifier = parseInt(osc.substring(0, idx));
+              const content = osc.substring(idx + 1);
               callback = this._oscHandlers[identifier];
               if (callback) callback(content);
               else this._oscHandlerFb(identifier, content);
diff --git a/src/EventEmitter.ts b/src/EventEmitter.ts
index 0698386e..9ce31bb5 100644
--- a/src/EventEmitter.ts
+++ b/src/EventEmitter.ts
@@ -44,7 +44,7 @@ export class EventEmitter implements IEventEmitter, IDisposable {
       return;
     }
 
-    let obj = this._events[type];
+    const obj = this._events[type];
     let i = obj.length;
 
     while (i--) {
@@ -65,7 +65,7 @@ export class EventEmitter implements IEventEmitter, IDisposable {
     if (!this._events[type]) {
       return;
     }
-    let obj = this._events[type];
+    const obj = this._events[type];
     for (let i = 0; i < obj.length; i++) {
       obj[i].apply(this, args);
     }
diff --git a/src/InputHandler.test.ts b/src/InputHandler.test.ts
index ddb16786..6dc043db 100644
--- a/src/InputHandler.test.ts
+++ b/src/InputHandler.test.ts
@@ -9,10 +9,10 @@ import { MockInputHandlingTerminal } from './utils/TestUtils.test';
 
 describe('InputHandler', () => {
   describe('save and restore cursor', () => {
-    let terminal = new MockInputHandlingTerminal();
+    const terminal = new MockInputHandlingTerminal();
     terminal.buffer.x = 1;
     terminal.buffer.y = 2;
-    let inputHandler = new InputHandler(terminal);
+    const inputHandler = new InputHandler(terminal);
     // Save cursor position
     inputHandler.saveCursor([]);
     assert.equal(terminal.buffer.x, 1);
@@ -27,8 +27,8 @@ describe('InputHandler', () => {
   });
   describe('setCursorStyle', () => {
     it('should call Terminal.setOption with correct params', () => {
-      let terminal = new MockInputHandlingTerminal();
-      let inputHandler = new InputHandler(terminal);
+      const terminal = new MockInputHandlingTerminal();
+      const inputHandler = new InputHandler(terminal);
       const collect = ' ';
 
       inputHandler.setCursorStyle([0], collect);
@@ -68,10 +68,10 @@ describe('InputHandler', () => {
   });
   describe('setMode', () => {
     it('should toggle Terminal.bracketedPasteMode', () => {
-      let terminal = new MockInputHandlingTerminal();
+      const terminal = new MockInputHandlingTerminal();
       const collect = '?';
       terminal.bracketedPasteMode = false;
-      let inputHandler = new InputHandler(terminal);
+      const inputHandler = new InputHandler(terminal);
       // Set bracketed paste mode
       inputHandler.setMode([2004], collect);
       assert.equal(terminal.bracketedPasteMode, true);
diff --git a/src/InputHandler.ts b/src/InputHandler.ts
index 7b12b6de..f5db133f 100644
--- a/src/InputHandler.ts
+++ b/src/InputHandler.ts
@@ -70,7 +70,7 @@ class DECRQSS implements IDcsHandler {
       case '"p': // DECSCL
         return this._terminal.send(`${C0.ESC}P1$r61"p${C0.ESC}\\`);
       case 'r': // DECSTBM
-        let pt = '' + (this._terminal.buffer.scrollTop + 1) +
+        const pt = '' + (this._terminal.buffer.scrollTop + 1) +
                 ';' + (this._terminal.buffer.scrollBottom + 1) + 'r';
         return this._terminal.send(`${C0.ESC}P1$r${pt}${C0.ESC}\\`);
       case 'm': // SGR
@@ -259,7 +259,7 @@ export class InputHandler implements IInputHandler {
     this._parser.setEscHandler('~', () => this.setgLevel(1));
     this._parser.setEscHandler('%@', () => this.selectDefaultCharset());
     this._parser.setEscHandler('%G', () => this.selectDefaultCharset());
-    for (let flag in CHARSETS) {
+    for (const flag in CHARSETS) {
       this._parser.setEscHandler('(' + flag, () => this.selectCharset('(' + flag));
       this._parser.setEscHandler(')' + flag, () => this.selectCharset(')' + flag));
       this._parser.setEscHandler('*' + flag, () => this.selectCharset('*' + flag));
@@ -416,7 +416,7 @@ export class InputHandler implements IInputHandler {
         for (let moves = 0; moves < chWidth; ++moves) {
           // remove last cell
           // if it's width is 0, we have to adjust the second last cell as well
-          let removed = bufferRow.pop();
+          const removed = bufferRow.pop();
           if (removed[CHAR_DATA_WIDTH_INDEX] === 0
               && bufferRow[this._terminal.cols - 2]
               && bufferRow[this._terminal.cols - 2][CHAR_DATA_WIDTH_INDEX] === 2) {
@@ -786,10 +786,10 @@ export class InputHandler implements IInputHandler {
     // make buffer local for faster access
     const buffer = this._terminal.buffer;
 
-    let row: number = buffer.y + buffer.ybase;
+    const row: number = buffer.y + buffer.ybase;
 
-    let scrollBottomRowsOffset = this._terminal.rows - 1 - buffer.scrollBottom;
-    let scrollBottomAbsolute = this._terminal.rows - 1 + buffer.ybase - scrollBottomRowsOffset + 1;
+    const scrollBottomRowsOffset = this._terminal.rows - 1 - buffer.scrollBottom;
+    const scrollBottomAbsolute = this._terminal.rows - 1 + buffer.ybase - scrollBottomRowsOffset + 1;
     while (param--) {
       // test: echo -e '\e[44m\e[1L\e[0m'
       // blankLine(true) - xterm/linux behavior
@@ -1107,7 +1107,7 @@ export class InputHandler implements IInputHandler {
    *   http://vt100.net/annarbor/aaa-ug/section6.html
    */
   public tabClear(params: number[]): void {
-    let param = params[0];
+    const param = params[0];
     if (param <= 0) {
       delete this._terminal.buffer.tabs[this._terminal.buffer.x];
     } else if (param === 3) {
diff --git a/src/Linkifier.test.ts b/src/Linkifier.test.ts
index 61245296..12d40bfe 100644
--- a/src/Linkifier.test.ts
+++ b/src/Linkifier.test.ts
@@ -47,7 +47,7 @@ describe('Linkifier', () => {
   });
 
   function stringToRow(text: string): LineData {
-    let result: LineData = [];
+    const result: LineData = [];
     for (let i = 0; i < text.length; i++) {
       result.push([0, text.charAt(i), 1, text.charCodeAt(i)]);
     }
diff --git a/src/Linkifier.ts b/src/Linkifier.ts
index 2a19c8d8..ee7c2626 100644
--- a/src/Linkifier.ts
+++ b/src/Linkifier.ts
@@ -199,11 +199,11 @@ export class Linkifier extends EventEmitter implements ILinkifier {
    */
   private _doLinkifyRow(rowIndex: number, text: string, matcher: ILinkMatcher, offset: number = 0): void {
     // Find the first match
-    let match = text.match(matcher.regex);
+    const match = text.match(matcher.regex);
     if (!match || match.length === 0) {
       return;
     }
-    let uri = match[typeof matcher.matchIndex !== 'number' ? 0 : matcher.matchIndex];
+    const uri = match[typeof matcher.matchIndex !== 'number' ? 0 : matcher.matchIndex];
 
     // Get index, match.index is for the outer match which includes negated chars
     const index = text.indexOf(uri);
diff --git a/src/SelectionManager.test.ts b/src/SelectionManager.test.ts
index 8d0b04aa..06cea766 100644
--- a/src/SelectionManager.test.ts
+++ b/src/SelectionManager.test.ts
@@ -51,7 +51,7 @@ describe('SelectionManager', () => {
   });
 
   function stringToRow(text: string): LineData {
-    let result: LineData = [];
+    const result: LineData = [];
     for (let i = 0; i < text.length; i++) {
       result.push([0, text.charAt(i), 1, text.charCodeAt(i)]);
     }
diff --git a/src/SelectionManager.ts b/src/SelectionManager.ts
index 93da887a..c150554f 100644
--- a/src/SelectionManager.ts
+++ b/src/SelectionManager.ts
@@ -179,7 +179,7 @@ export class SelectionManager extends EventEmitter implements ISelectionManager
 
     // Get first row
     const startRowEndCol = start[1] === end[1] ? end[0] : null;
-    let result: string[] = [];
+    const result: string[] = [];
     result.push(this._buffer.translateBufferLineToString(start[1], true, start[0], startRowEndCol));
 
     // Get middle rows
@@ -586,7 +586,7 @@ export class SelectionManager extends EventEmitter implements ISelectionManager
    * @param event The mouseup event.
    */
   private _onMouseUp(event: MouseEvent): void {
-    let timeElapsed = event.timeStamp - this._mouseDownTimeStamp;
+    const timeElapsed = event.timeStamp - this._mouseDownTimeStamp;
 
     this._removeMouseDownListeners();
 
diff --git a/src/Terminal.integration.ts b/src/Terminal.integration.ts
index fdf27acf..54e76518 100644
--- a/src/Terminal.integration.ts
+++ b/src/Terminal.integration.ts
@@ -24,8 +24,8 @@ let primitivePty: any;
 function ptyWriteRead(data: string, cb: (result: string) => void): void {
   fs.writeSync(primitivePty.slave, data);
   setTimeout(() => {
-    let b = new Buffer(64000);
-    let bytes = fs.readSync(primitivePty.master, b, 0, 64000, null);
+    const b = new Buffer(64000);
+    const bytes = fs.readSync(primitivePty.master, b, 0, 64000, null);
     cb(b.toString('utf8', 0, bytes));
   });
 }
@@ -45,7 +45,7 @@ function formatError(input: string, output: string, expected: string): string {
       return '\x1b[33m' + (' ' + counter).slice(-2) + color + s;
     };
   }
-  let line80 = '12345678901234567890123456789012345678901234567890123456789012345678901234567890';
+  const line80 = '12345678901234567890123456789012345678901234567890123456789012345678901234567890';
   let s = '';
   s += '\n\x1b[34m' + JSON.stringify(input);
   s += '\n\x1b[33m  ' + line80 + '\n';
@@ -74,11 +74,11 @@ function terminalToString(term: Terminal): string {
 
 // Skip tests on Windows since pty.open isn't supported
 if (os.platform() !== 'win32') {
-  let CONSOLE_LOG = console.log;
+  const CONSOLE_LOG = console.log;
 
   // expect files need terminal at 80x25!
-  let COLS = 80;
-  let ROWS = 25;
+  const COLS = 80;
+  const ROWS = 25;
 
   /** some helpers for pty interaction */
   // we need a pty in between to get the termios decorations
@@ -99,9 +99,9 @@ if (os.platform() !== 'win32') {
 
     // omit stack trace for escape sequence files
     Error.stackTraceLimit = 0;
-    let files = glob.sync('**/escape_sequence_files/*.in', { cwd: path.join(__dirname, '..')});
+    const files = glob.sync('**/escape_sequence_files/*.in', { cwd: path.join(__dirname, '..')});
     // only successful tests for now
-    let skip = [
+    const skip = [
       10, 16, 17, 19, 32, 33, 34, 35, 36, 39,
       40, 42, 43, 44, 45, 46, 47, 48, 49, 50,
       51, 52, 54, 55, 56, 57, 58, 59, 60, 61,
@@ -118,7 +118,7 @@ if (os.platform() !== 'win32') {
       ((filename: string) => {
         it(filename.split('/').slice(-1)[0], done => {
           ptyReset(() => {
-            let inFile = fs.readFileSync(filename, 'utf8');
+            const inFile = fs.readFileSync(filename, 'utf8');
             ptyWriteRead(inFile, fromPty => {
               // uncomment this to get log from terminal
               // console.log = function(){};
@@ -127,12 +127,12 @@ if (os.platform() !== 'win32') {
               xterm.writeBuffer.push(fromPty);
               xterm._innerWrite();
 
-              let fromEmulator = terminalToString(xterm);
+              const fromEmulator = terminalToString(xterm);
               console.log = CONSOLE_LOG;
-              let expected = fs.readFileSync(filename.split('.')[0] + '.text', 'utf8');
+              const expected = fs.readFileSync(filename.split('.')[0] + '.text', 'utf8');
               // Some of the tests have whitespace on the right of lines, we trim all the linex
               // from xterm.js so ignore this for now at least.
-              let expectedRightTrimmed = expected.split('\n').map(l => l.replace(/\s+$/, '')).join('\n');
+              const expectedRightTrimmed = expected.split('\n').map(l => l.replace(/\s+$/, '')).join('\n');
               if (fromEmulator !== expectedRightTrimmed) {
                 // uncomment to get noisy output
                 throw new Error(formatError(inFile, fromEmulator, expected));
@@ -155,7 +155,7 @@ describe('typings', () => {
       tsc += '.cmd';
     }
     const fixtureDir = path.join(__dirname, '..', 'fixtures', 'typings-test');
-    let result = cp.spawnSync(tsc, { cwd: fixtureDir });
+    const result = cp.spawnSync(tsc, { cwd: fixtureDir });
     assert.equal(result.status, 0, `build did not succeed:\nstdout: ${result.stdout.toString()}\nstderr: ${result.stderr.toString()}\n`);
     // Clean up
     fs.unlinkSync(path.join(fixtureDir, 'typings-test.js'));
diff --git a/src/Terminal.test.ts b/src/Terminal.test.ts
index 5a604379..5b7039e9 100644
--- a/src/Terminal.test.ts
+++ b/src/Terminal.test.ts
@@ -77,13 +77,13 @@ describe('term.js addons', () => {
   });
 
   describe('attachCustomKeyEventHandler', () => {
-    let evKeyDown = <KeyboardEvent>{
+    const evKeyDown = <KeyboardEvent>{
       preventDefault: () => {},
       stopPropagation: () => {},
       type: 'keydown',
       keyCode: 77
     };
-    let evKeyPress = <KeyboardEvent>{
+    const evKeyPress = <KeyboardEvent>{
       preventDefault: () => {},
       stopPropagation: () => {},
       type: 'keypress',
@@ -131,7 +131,7 @@ describe('term.js addons', () => {
 
   describe('clear', () => {
     it('should clear a buffer equal to rows', () => {
-      let promptLine = term.buffer.lines.get(term.buffer.ybase + term.buffer.y);
+      const promptLine = term.buffer.lines.get(term.buffer.ybase + term.buffer.y);
       term.clear();
       assert.equal(term.buffer.y, 0);
       assert.equal(term.buffer.ybase, 0);
@@ -148,7 +148,7 @@ describe('term.js addons', () => {
         term.write('test\n');
       }
 
-      let promptLine = term.buffer.lines.get(term.buffer.ybase + term.buffer.y);
+      const promptLine = term.buffer.lines.get(term.buffer.ybase + term.buffer.y);
       term.clear();
       assert.equal(term.buffer.y, 0);
       assert.equal(term.buffer.ybase, 0);
@@ -160,7 +160,7 @@ describe('term.js addons', () => {
       }
     });
     it('should not break the prompt when cleared twice', () => {
-      let promptLine = term.buffer.lines.get(term.buffer.ybase + term.buffer.y);
+      const promptLine = term.buffer.lines.get(term.buffer.ybase + term.buffer.y);
       term.clear();
       term.clear();
       assert.equal(term.buffer.y, 0);
@@ -302,7 +302,7 @@ describe('term.js addons', () => {
         (<any>term)._evaluateKeyEscapeSequence = () => {
           return { key: 'a' };
         };
-        let event = <KeyboardEvent>{
+        const event = <KeyboardEvent>{
           type: 'keydown',
           keyCode: 0,
           preventDefault: () => {},
@@ -322,7 +322,7 @@ describe('term.js addons', () => {
         for (let i = 0; i < term.rows * 3; i++) {
           term.writeln('test');
         }
-        let startYDisp = (term.rows * 2) + 1;
+        const startYDisp = (term.rows * 2) + 1;
         term.attachCustomKeyEventHandler(() => {
           return false;
         });
@@ -784,11 +784,11 @@ describe('term.js addons', () => {
       });
 
       it('should emit key with alt + key on keyPress', (done) => {
-        let keys = ['@', '@', '\\', '\\', '|', '|'];
+        const keys = ['@', '@', '\\', '\\', '|', '|'];
 
         term.on('keypress', (key) => {
           if (key) {
-            let index = keys.indexOf(key);
+            const index = keys.indexOf(key);
             assert(index !== -1, 'Emitted wrong key: ' + key);
             keys.splice(index, 1);
           }
@@ -850,11 +850,11 @@ describe('term.js addons', () => {
       });
 
       it('should emit key with alt + ctrl + key on keyPress', (done) => {
-        let keys = ['@', '@', '\\', '\\', '|', '|'];
+        const keys = ['@', '@', '\\', '\\', '|', '|'];
 
         term.on('keypress', (key) => {
           if (key) {
-            let index = keys.indexOf(key);
+            const index = keys.indexOf(key);
             assert(index !== -1, 'Emitted wrong key: ' + key);
             keys.splice(index, 1);
           }
@@ -895,10 +895,10 @@ describe('term.js addons', () => {
   describe('unicode - surrogates', () => {
     it('2 characters per cell', function (): void {
       this.timeout(10000);  // This is needed because istanbul patches code and slows it down
-      let high = String.fromCharCode(0xD800);
+      const high = String.fromCharCode(0xD800);
       for (let i = 0xDC00; i <= 0xDCFF; ++i) {
         term.write(high + String.fromCharCode(i));
-        let tchar = term.buffer.lines.get(0)[0];
+        const tchar = term.buffer.lines.get(0)[0];
         expect(tchar[CHAR_DATA_CHAR_INDEX]).eql(high + String.fromCharCode(i));
         expect(tchar[CHAR_DATA_CHAR_INDEX].length).eql(2);
         expect(tchar[CHAR_DATA_WIDTH_INDEX]).eql(1);
@@ -907,7 +907,7 @@ describe('term.js addons', () => {
       }
     });
     it('2 characters at last cell', () => {
-      let high = String.fromCharCode(0xD800);
+      const high = String.fromCharCode(0xD800);
       for (let i = 0xDC00; i <= 0xDCFF; ++i) {
         term.buffer.x = term.cols - 1;
         term.write(high + String.fromCharCode(i));
@@ -918,7 +918,7 @@ describe('term.js addons', () => {
       }
     });
     it('2 characters per cell over line end with autowrap', () => {
-      let high = String.fromCharCode(0xD800);
+      const high = String.fromCharCode(0xD800);
       for (let i = 0xDC00; i <= 0xDCFF; ++i) {
         term.buffer.x = term.cols - 1;
         term.wraparoundMode = true;
@@ -931,7 +931,7 @@ describe('term.js addons', () => {
       }
     });
     it('2 characters per cell over line end without autowrap', () => {
-      let high = String.fromCharCode(0xD800);
+      const high = String.fromCharCode(0xD800);
       for (let i = 0xDC00; i <= 0xDCFF; ++i) {
         term.buffer.x = term.cols - 1;
         term.wraparoundMode = false;
@@ -944,11 +944,11 @@ describe('term.js addons', () => {
       }
     });
     it('splitted surrogates', () => {
-      let high = String.fromCharCode(0xD800);
+      const high = String.fromCharCode(0xD800);
       for (let i = 0xDC00; i <= 0xDCFF; ++i) {
         term.write(high);
         term.write(String.fromCharCode(i));
-        let tchar = term.buffer.lines.get(0)[0];
+        const tchar = term.buffer.lines.get(0)[0];
         expect(tchar[CHAR_DATA_CHAR_INDEX]).eql(high + String.fromCharCode(i));
         expect(tchar[CHAR_DATA_CHAR_INDEX].length).eql(2);
         expect(tchar[CHAR_DATA_WIDTH_INDEX]).eql(1);
@@ -979,12 +979,12 @@ describe('term.js addons', () => {
       term.wraparoundMode = true;
       term.write(Array(100).join('e\u0301'));
       for (let i = 0; i < term.cols; ++i) {
-        let tchar = term.buffer.lines.get(0)[i];
+        const tchar = term.buffer.lines.get(0)[i];
         expect(tchar[CHAR_DATA_CHAR_INDEX]).eql('e\u0301');
         expect(tchar[CHAR_DATA_CHAR_INDEX].length).eql(2);
         expect(tchar[CHAR_DATA_WIDTH_INDEX]).eql(1);
       }
-      let tchar = term.buffer.lines.get(1)[0];
+      const tchar = term.buffer.lines.get(1)[0];
       expect(tchar[CHAR_DATA_CHAR_INDEX]).eql('e\u0301');
       expect(tchar[CHAR_DATA_CHAR_INDEX].length).eql(2);
       expect(tchar[CHAR_DATA_WIDTH_INDEX]).eql(1);
@@ -993,12 +993,12 @@ describe('term.js addons', () => {
       term.wraparoundMode = true;
       term.write(Array(100).join('\uD800\uDC00\u0301'));
       for (let i = 0; i < term.cols; ++i) {
-        let tchar = term.buffer.lines.get(0)[i];
+        const tchar = term.buffer.lines.get(0)[i];
         expect(tchar[CHAR_DATA_CHAR_INDEX]).eql('\uD800\uDC00\u0301');
         expect(tchar[CHAR_DATA_CHAR_INDEX].length).eql(3);
         expect(tchar[CHAR_DATA_WIDTH_INDEX]).eql(1);
       }
-      let tchar = term.buffer.lines.get(1)[0];
+      const tchar = term.buffer.lines.get(1)[0];
       expect(tchar[CHAR_DATA_CHAR_INDEX]).eql('\uD800\uDC00\u0301');
       expect(tchar[CHAR_DATA_CHAR_INDEX].length).eql(3);
       expect(tchar[CHAR_DATA_WIDTH_INDEX]).eql(1);
@@ -1021,7 +1021,7 @@ describe('term.js addons', () => {
       term.wraparoundMode = true;
       term.write(Array(50).join('￥'));
       for (let i = 0; i < term.cols; ++i) {
-        let tchar = term.buffer.lines.get(0)[i];
+        const tchar = term.buffer.lines.get(0)[i];
         if (i % 2) {
           expect(tchar[CHAR_DATA_CHAR_INDEX]).eql('');
           expect(tchar[CHAR_DATA_CHAR_INDEX].length).eql(0);
@@ -1032,7 +1032,7 @@ describe('term.js addons', () => {
           expect(tchar[CHAR_DATA_WIDTH_INDEX]).eql(2);
         }
       }
-      let tchar = term.buffer.lines.get(1)[0];
+      const tchar = term.buffer.lines.get(1)[0];
       expect(tchar[CHAR_DATA_CHAR_INDEX]).eql('￥');
       expect(tchar[CHAR_DATA_CHAR_INDEX].length).eql(1);
       expect(tchar[CHAR_DATA_WIDTH_INDEX]).eql(2);
@@ -1042,7 +1042,7 @@ describe('term.js addons', () => {
       term.buffer.x = 1;
       term.write(Array(50).join('￥'));
       for (let i = 1; i < term.cols - 1; ++i) {
-        let tchar = term.buffer.lines.get(0)[i];
+        const tchar = term.buffer.lines.get(0)[i];
         if (!(i % 2)) {
           expect(tchar[CHAR_DATA_CHAR_INDEX]).eql('');
           expect(tchar[CHAR_DATA_CHAR_INDEX].length).eql(0);
@@ -1067,7 +1067,7 @@ describe('term.js addons', () => {
       term.buffer.x = 1;
       term.write(Array(50).join('￥\u0301'));
       for (let i = 1; i < term.cols - 1; ++i) {
-        let tchar = term.buffer.lines.get(0)[i];
+        const tchar = term.buffer.lines.get(0)[i];
         if (!(i % 2)) {
           expect(tchar[CHAR_DATA_CHAR_INDEX]).eql('');
           expect(tchar[CHAR_DATA_CHAR_INDEX].length).eql(0);
@@ -1091,7 +1091,7 @@ describe('term.js addons', () => {
       term.wraparoundMode = true;
       term.write(Array(50).join('￥\u0301'));
       for (let i = 0; i < term.cols; ++i) {
-        let tchar = term.buffer.lines.get(0)[i];
+        const tchar = term.buffer.lines.get(0)[i];
         if (i % 2) {
           expect(tchar[CHAR_DATA_CHAR_INDEX]).eql('');
           expect(tchar[CHAR_DATA_CHAR_INDEX].length).eql(0);
@@ -1102,7 +1102,7 @@ describe('term.js addons', () => {
           expect(tchar[CHAR_DATA_WIDTH_INDEX]).eql(2);
         }
       }
-      let tchar = term.buffer.lines.get(1)[0];
+      const tchar = term.buffer.lines.get(1)[0];
       expect(tchar[CHAR_DATA_CHAR_INDEX]).eql('￥\u0301');
       expect(tchar[CHAR_DATA_CHAR_INDEX].length).eql(2);
       expect(tchar[CHAR_DATA_WIDTH_INDEX]).eql(2);
@@ -1112,7 +1112,7 @@ describe('term.js addons', () => {
       term.buffer.x = 1;
       term.write(Array(50).join('\ud843\ude6d\u0301'));
       for (let i = 1; i < term.cols - 1; ++i) {
-        let tchar = term.buffer.lines.get(0)[i];
+        const tchar = term.buffer.lines.get(0)[i];
         if (!(i % 2)) {
           expect(tchar[CHAR_DATA_CHAR_INDEX]).eql('');
           expect(tchar[CHAR_DATA_CHAR_INDEX].length).eql(0);
@@ -1136,7 +1136,7 @@ describe('term.js addons', () => {
       term.wraparoundMode = true;
       term.write(Array(50).join('\ud843\ude6d\u0301'));
       for (let i = 0; i < term.cols; ++i) {
-        let tchar = term.buffer.lines.get(0)[i];
+        const tchar = term.buffer.lines.get(0)[i];
         if (i % 2) {
           expect(tchar[CHAR_DATA_CHAR_INDEX]).eql('');
           expect(tchar[CHAR_DATA_CHAR_INDEX].length).eql(0);
@@ -1147,7 +1147,7 @@ describe('term.js addons', () => {
           expect(tchar[CHAR_DATA_WIDTH_INDEX]).eql(2);
         }
       }
-      let tchar = term.buffer.lines.get(1)[0];
+      const tchar = term.buffer.lines.get(1)[0];
       expect(tchar[CHAR_DATA_CHAR_INDEX]).eql('\ud843\ude6d\u0301');
       expect(tchar[CHAR_DATA_CHAR_INDEX].length).eql(3);
       expect(tchar[CHAR_DATA_WIDTH_INDEX]).eql(2);
diff --git a/src/Terminal.ts b/src/Terminal.ts
index 2cae7b56..63f7efdb 100644
--- a/src/Terminal.ts
+++ b/src/Terminal.ts
@@ -827,7 +827,7 @@ export class Terminal extends EventEmitter implements ITerminal, IDisposable, II
     // ^[[M 3<^[[M@4<^[[M@5<^[[M@6<^[[M@7<^[[M#7<
     function sendMove(ev: MouseEvent): void {
       let button = pressed;
-      let pos = self.mouseHelper.getRawByteCoords(ev, self.screenElement, self.charMeasure, self.options.lineHeight, self.cols, self.rows);
+      const pos = self.mouseHelper.getRawByteCoords(ev, self.screenElement, self.charMeasure, self.options.lineHeight, self.cols, self.rows);
       if (!pos) return;
 
       // buttons marked as motions
@@ -938,7 +938,7 @@ export class Terminal extends EventEmitter implements ITerminal, IDisposable, II
         return;
       }
 
-      let data: number[] = [];
+      const data: number[] = [];
 
       encode(data, button);
       encode(data, pos.x);
@@ -1145,7 +1145,7 @@ export class Terminal extends EventEmitter implements ITerminal, IDisposable, II
   public scroll(isWrapped?: boolean): void {
     const newLine = this.blankLine(undefined, isWrapped);
     const topRow = this.buffer.ybase + this.buffer.scrollTop;
-    let bottomRow = this.buffer.ybase + this.buffer.scrollBottom;
+    const bottomRow = this.buffer.ybase + this.buffer.scrollBottom;
 
     if (this.buffer.scrollTop === 0) {
       // Determine whether the buffer is going to be trimmed after insertion.
diff --git a/src/Viewport.ts b/src/Viewport.ts
index c951d6b5..f690c348 100644
--- a/src/Viewport.ts
+++ b/src/Viewport.ts
@@ -180,7 +180,7 @@ export class Viewport implements IViewport {
    * @param ev The touch event.
    */
   public onTouchMove(ev: TouchEvent): void {
-    let deltaY = this._lastTouchY - ev.touches[0].pageY;
+    const deltaY = this._lastTouchY - ev.touches[0].pageY;
     this._lastTouchY = ev.touches[0].pageY;
     if (deltaY === 0) {
       return;
diff --git a/src/addons/attach/attach.ts b/src/addons/attach/attach.ts
index 4a9668de..731739f4 100644
--- a/src/addons/attach/attach.ts
+++ b/src/addons/attach/attach.ts
@@ -51,7 +51,7 @@ export function attach(term: Terminal, socket: WebSocket, bidirectional: boolean
         str = myTextDecoder.decode(ev.data);
         displayData(str);
       } else {
-        let fileReader = new FileReader();
+        const fileReader = new FileReader();
 
         fileReader.addEventListener('load', () => {
           str = myTextDecoder.decode(this.result);
diff --git a/src/addons/webLinks/webLinks.test.ts b/src/addons/webLinks/webLinks.test.ts
index b3c76703..c84ee1a5 100644
--- a/src/addons/webLinks/webLinks.test.ts
+++ b/src/addons/webLinks/webLinks.test.ts
@@ -34,8 +34,8 @@ describe('webLinks addon', () => {
 
     const row = '  http://foo.com/a~b#c~d?e~f  ';
 
-    let match = row.match(term.regex);
-    let uri = match[term.options.matchIndex];
+    const match = row.match(term.regex);
+    const uri = match[term.options.matchIndex];
 
     assert.equal(uri, 'http://foo.com/a~b#c~d?e~f');
   });
diff --git a/src/handlers/AltClickHandler.ts b/src/handlers/AltClickHandler.ts
index 7f2e4f05..8f1cf2df 100644
--- a/src/handlers/AltClickHandler.ts
+++ b/src/handlers/AltClickHandler.ts
@@ -28,7 +28,7 @@ export class AltClickHandler {
     this._startCol = this._terminal.buffer.x;
     this._startRow = this._terminal.buffer.y;
 
-    let coordinates = this._terminal.mouseHelper.getCoords(
+    const coordinates = this._terminal.mouseHelper.getCoords(
       this._mouseEvent,
       this._terminal.element,
       this._terminal.charMeasure,
@@ -89,10 +89,10 @@ export class AltClickHandler {
    * ignoring wrapped rows
    */
   private _moveToRequestedRow(): string {
-    let startRow = this._startRow - this._wrappedRowsForRow(this._startRow);
-    let endRow = this._endRow - this._wrappedRowsForRow(this._endRow);
+    const startRow = this._startRow - this._wrappedRowsForRow(this._startRow);
+    const endRow = this._endRow - this._wrappedRowsForRow(this._endRow);
 
-    let rowsToMove = Math.abs(startRow - endRow) - this._wrappedRowsCount();
+    const rowsToMove = Math.abs(startRow - endRow) - this._wrappedRowsCount();
 
     return repeat(rowsToMove, this._sequence(this._verticalDirection()));
   }
@@ -108,8 +108,8 @@ export class AltClickHandler {
       startRow = this._startRow;
     }
 
-    let endRow = this._endRow;
-    let direction = this._horizontalDirection();
+    const endRow = this._endRow;
+    const direction = this._horizontalDirection();
 
     return repeat(this._bufferLine(
       this._startCol, startRow, this._endCol, endRow,
@@ -118,7 +118,7 @@ export class AltClickHandler {
   }
 
   private _moveHorizontallyOnly(): string {
-    let direction = this._horizontalDirection();
+    const direction = this._horizontalDirection();
     return repeat(Math.abs(this._startCol - this._endCol), this._sequence(direction));
   }
 
@@ -132,11 +132,11 @@ export class AltClickHandler {
    */
   private _wrappedRowsCount(): number {
     let wrappedRows = 0;
-    let startRow = this._startRow - this._wrappedRowsForRow(this._startRow);
-    let endRow = this._endRow - this._wrappedRowsForRow(this._endRow);
+    const startRow = this._startRow - this._wrappedRowsForRow(this._startRow);
+    const endRow = this._endRow - this._wrappedRowsForRow(this._endRow);
 
     for (let i = 0; i < Math.abs(startRow - endRow); i++) {
-      let direction = this._verticalDirection() === Direction.UP ? -1 : 1;
+      const direction = this._verticalDirection() === Direction.UP ? -1 : 1;
 
       if ((<any>this._lines.get(startRow + (direction * i))).isWrapped) {
         wrappedRows++;
diff --git a/src/handlers/Clipboard.ts b/src/handlers/Clipboard.ts
index 23925007..bbb8302c 100644
--- a/src/handlers/Clipboard.ts
+++ b/src/handlers/Clipboard.ts
@@ -58,7 +58,7 @@ export function pasteHandler(ev: ClipboardEvent, term: ITerminal): void {
 
   let text: string;
 
-  let dispatchPaste = function(text: string): void {
+  const dispatchPaste = function(text: string): void {
     text = prepareTextForTerminal(text);
     text = bracketTextForPaste(text, term.bracketedPasteMode);
     term.handler(text);
diff --git a/src/renderer/ColorManager.test.ts b/src/renderer/ColorManager.test.ts
index 724bc758..0012c1ed 100644
--- a/src/renderer/ColorManager.test.ts
+++ b/src/renderer/ColorManager.test.ts
@@ -33,7 +33,7 @@ describe('ColorManager', () => {
 
   describe('constructor', () => {
     it('should fill all colors with values', () => {
-      for (let key of Object.keys(cm.colors)) {
+      for (const key of Object.keys(cm.colors)) {
         if (key !== 'ansi') {
           // A #rrggbb or rgba(...)
           assert.ok(cm.colors[key].css.length >= 7);
diff --git a/src/renderer/ColorManager.ts b/src/renderer/ColorManager.ts
index 9ab60750..d169f266 100644
--- a/src/renderer/ColorManager.ts
+++ b/src/renderer/ColorManager.ts
@@ -42,7 +42,7 @@ export const DEFAULT_ANSI_COLORS = (() => {
 
   // Fill in the remaining 240 ANSI colors.
   // Generate colors (16-231)
-  let v = [0x00, 0x5f, 0x87, 0xaf, 0xd7, 0xff];
+  const v = [0x00, 0x5f, 0x87, 0xaf, 0xd7, 0xff];
   for (let i = 0; i < 216; i++) {
     const r = v[(i / 36) % 6 | 0];
     const g = v[(i / 6) % 6 | 0];
@@ -75,7 +75,7 @@ function fromHex(css: string): IColor {
 }
 
 function toPaddedHex(c: number): string {
-  let s = c.toString(16);
+  const s = c.toString(16);
   return s.length < 2 ? '0' + s : s;
 }
 
diff --git a/src/utils/CircularList.ts b/src/utils/CircularList.ts
index 1f00ea09..ca83d6e1 100644
--- a/src/utils/CircularList.ts
+++ b/src/utils/CircularList.ts
@@ -36,7 +36,7 @@ export class CircularList<T> extends EventEmitter implements ICircularList<T> {
 
     // Reconstruct array, starting at index 0. Only transfer values from the
     // indexes 0 to length.
-    let newArray = new Array<T>(newMaxLength);
+    const newArray = new Array<T>(newMaxLength);
     for (let i = 0; i < Math.min(newMaxLength, this.length); i++) {
       newArray[i] = this._array[this._getCyclicIndex(i)];
     }
diff --git a/tslint.json b/tslint.json
index 67dc7955..8b364077 100644
--- a/tslint.json
+++ b/tslint.json
@@ -101,6 +101,7 @@
     },
     "prefer-const-enum": [
       true
-    ]
+    ],
+    "prefer-const": true
   }
 }