diff --git a/addons/xterm-addon-attach/src/AttachAddon.ts b/addons/xterm-addon-attach/src/AttachAddon.ts
index 279d1b2e..035807ae 100644
--- a/addons/xterm-addon-attach/src/AttachAddon.ts
+++ b/addons/xterm-addon-attach/src/AttachAddon.ts
@@ -41,7 +41,9 @@ export class AttachAddon implements ITerminalAddon {
   }
 
   public dispose(): void {
-    this._disposables.forEach(d => d.dispose());
+    for (const d of this._disposables) {
+      d.dispose();
+    }
   }
 
   private _sendData(data: string): void {
diff --git a/addons/xterm-addon-attach/test/AttachAddon.api.ts b/addons/xterm-addon-attach/test/AttachAddon.api.ts
index 41e579f5..2dea645f 100644
--- a/addons/xterm-addon-attach/test/AttachAddon.api.ts
+++ b/addons/xterm-addon-attach/test/AttachAddon.api.ts
@@ -18,7 +18,7 @@ describe('AttachAddon', () => {
   before(async function(): Promise<any> {
     const browserType = getBrowserType();
     browser = await browserType.launch({
-      headless: process.argv.indexOf('--headless') !== -1
+      headless: process.argv.includes('--headless')
     });
     page = await (await browser.newContext()).newPage();
     await page.setViewportSize({ width, height });
diff --git a/addons/xterm-addon-fit/test/FitAddon.api.ts b/addons/xterm-addon-fit/test/FitAddon.api.ts
index 1111dff0..5a5b3264 100644
--- a/addons/xterm-addon-fit/test/FitAddon.api.ts
+++ b/addons/xterm-addon-fit/test/FitAddon.api.ts
@@ -18,7 +18,7 @@ describe('FitAddon', () => {
   before(async function(): Promise<any> {
     const browserType = getBrowserType();
     browser = await browserType.launch({
-      headless: process.argv.indexOf('--headless') !== -1
+      headless: process.argv.includes('--headless')
     });
     page = await (await browser.newContext()).newPage();
     await page.setViewportSize({ width, height });
@@ -45,7 +45,7 @@ describe('FitAddon', () => {
 
   describe('proposeDimensions', () => {
     afterEach(async () => {
-      return unloadFit();
+      return await unloadFit();
     });
 
     it('default', async function(): Promise<any> {
@@ -84,7 +84,7 @@ describe('FitAddon', () => {
 
   describe('fit', () => {
     afterEach(async () => {
-      return unloadFit();
+      return await unloadFit();
     });
 
     it('default', async function(): Promise<any> {
diff --git a/addons/xterm-addon-ligatures/src/parse.ts b/addons/xterm-addon-ligatures/src/parse.ts
index 5ad7747f..6289e468 100644
--- a/addons/xterm-addon-ligatures/src/parse.ts
+++ b/addons/xterm-addon-ligatures/src/parse.ts
@@ -68,7 +68,7 @@ function parseString(context: IParseContext, quoteChar: '\'' | '"'): string {
   while (context.offset < context.input.length) {
     const char = context.input[context.offset++];
     if (escaped) {
-      if (/[0-9a-fA-F]/.test(char)) {
+      if (/[\dA-Fa-f]/.test(char)) {
         // Unicode escape
         context.offset--;
         str += parseUnicode(context);
@@ -107,7 +107,7 @@ function parseIdentifier(context: IParseContext): string {
   while (context.offset < context.input.length) {
     const char = context.input[context.offset++];
     if (escaped) {
-      if (/[0-9a-fA-F]/.test(char)) {
+      if (/[\dA-Fa-f]/.test(char)) {
         // Unicode escape
         context.offset--;
         str += parseUnicode(context);
@@ -156,7 +156,7 @@ function parseUnicode(context: IParseContext): string {
       // of the escape and is swallowed.
       return unicodeToString(str);
     }
-    if (str.length >= 6 || !/[0-9a-fA-F]/.test(char)) {
+    if (str.length >= 6 || !/[\dA-Fa-f]/.test(char)) {
       // If the next character is not a valid hex digit or we have reached the
       // maximum of 6 digits in the escape, terminate the escape.
       context.offset--;
diff --git a/addons/xterm-addon-search/src/SearchAddon.ts b/addons/xterm-addon-search/src/SearchAddon.ts
index efc12662..64e89bb3 100644
--- a/addons/xterm-addon-search/src/SearchAddon.ts
+++ b/addons/xterm-addon-search/src/SearchAddon.ts
@@ -240,8 +240,8 @@ export class SearchAddon implements ITerminalAddon {
    * @param term the substring that starts at searchIndex
    */
   private _isWholeWord(searchIndex: number, line: string, term: string): boolean {
-    return (((searchIndex === 0) || (NON_WORD_CHARACTERS.indexOf(line[searchIndex - 1]) !== -1)) &&
-      (((searchIndex + term.length) === line.length) || (NON_WORD_CHARACTERS.indexOf(line[searchIndex + term.length]) !== -1)));
+    return ((searchIndex === 0) || (NON_WORD_CHARACTERS.includes(line[searchIndex - 1]))) &&
+      (((searchIndex + term.length) === line.length) || (NON_WORD_CHARACTERS.includes(line[searchIndex + term.length])));
   }
 
   /**
@@ -262,7 +262,7 @@ export class SearchAddon implements ITerminalAddon {
 
     // Ignore wrapped lines, only consider on unwrapped line (first row of command string).
     const firstLine = terminal.buffer.active.getLine(row);
-    if (firstLine && firstLine.isWrapped) {
+    if (firstLine?.isWrapped) {
       if (isReverseSearch) {
         searchPosition.startCol += terminal.cols;
         return;
diff --git a/addons/xterm-addon-search/test/SearchAddon.api.ts b/addons/xterm-addon-search/test/SearchAddon.api.ts
index 3707aecd..b92dbc3a 100644
--- a/addons/xterm-addon-search/test/SearchAddon.api.ts
+++ b/addons/xterm-addon-search/test/SearchAddon.api.ts
@@ -20,7 +20,7 @@ describe('Search Tests', function(): void {
   before(async function(): Promise<any> {
     const browserType = getBrowserType();
     browser = await browserType.launch({
-      headless: process.argv.indexOf('--headless') !== -1
+      headless: process.argv.includes('--headless')
     });
     page = await (await browser.newContext()).newPage();
     await page.setViewportSize({ width, height });
diff --git a/addons/xterm-addon-serialize/test/SerializeAddon.api.ts b/addons/xterm-addon-serialize/test/SerializeAddon.api.ts
index 47af9d91..d472d753 100644
--- a/addons/xterm-addon-serialize/test/SerializeAddon.api.ts
+++ b/addons/xterm-addon-serialize/test/SerializeAddon.api.ts
@@ -34,7 +34,7 @@ describe('SerializeAddon', () => {
   before(async function(): Promise<any> {
     const browserType = getBrowserType();
     browser = await browserType.launch({
-      headless: process.argv.indexOf('--headless') !== -1
+      headless: process.argv.includes('--headless')
     });
     page = await (await browser.newContext()).newPage();
     await page.setViewportSize({ width, height });
diff --git a/addons/xterm-addon-unicode11/test/Unicode11Addon.api.ts b/addons/xterm-addon-unicode11/test/Unicode11Addon.api.ts
index d0e09da2..7369eeaa 100644
--- a/addons/xterm-addon-unicode11/test/Unicode11Addon.api.ts
+++ b/addons/xterm-addon-unicode11/test/Unicode11Addon.api.ts
@@ -18,7 +18,7 @@ describe('Unicode11Addon', () => {
   before(async function(): Promise<any> {
     const browserType = getBrowserType();
     browser = await browserType.launch({
-      headless: process.argv.indexOf('--headless') !== -1
+      headless: process.argv.includes('--headless')
     });
     page = await (await browser.newContext()).newPage();
     await page.setViewportSize({ width, height });
diff --git a/addons/xterm-addon-web-links/src/WebLinkProvider.ts b/addons/xterm-addon-web-links/src/WebLinkProvider.ts
index 487d5fe6..f0caf974 100644
--- a/addons/xterm-addon-web-links/src/WebLinkProvider.ts
+++ b/addons/xterm-addon-web-links/src/WebLinkProvider.ts
@@ -41,7 +41,7 @@ export class WebLinkProvider implements ILinkProvider {
 }
 
 export class LinkComputer {
-  public static computeLink(y: number, regex: RegExp, terminal: Terminal, handler: (event: MouseEvent, uri: string) => void): ILink[] {
+  public static computeLink(y: number, regex: RegExp, terminal: Terminal, activate: (event: MouseEvent, uri: string) => void): ILink[] {
     const rex = new RegExp(regex.source, (regex.flags || '') + 'g');
 
     const [line, startLineIndex] = LinkComputer._translateBufferLineToStringWithWrap(y - 1, false, terminal);
@@ -89,7 +89,7 @@ export class LinkComputer {
         }
       };
 
-      result.push({ range, text, activate: handler });
+      result.push({ range, text, activate });
     }
 
     return result;
diff --git a/addons/xterm-addon-web-links/test/WebLinksAddon.api.ts b/addons/xterm-addon-web-links/test/WebLinksAddon.api.ts
index 6e42ff96..47fd7911 100644
--- a/addons/xterm-addon-web-links/test/WebLinksAddon.api.ts
+++ b/addons/xterm-addon-web-links/test/WebLinksAddon.api.ts
@@ -18,7 +18,7 @@ describe('WebLinksAddon', () => {
   before(async function(): Promise<any> {
     const browserType = getBrowserType();
     browser = await browserType.launch({
-      headless: process.argv.indexOf('--headless') !== -1
+      headless: process.argv.includes('--headless')
     });
     page = await (await browser.newContext()).newPage();
     await page.setViewportSize({ width, height });
diff --git a/addons/xterm-addon-webgl/src/WebglRenderer.ts b/addons/xterm-addon-webgl/src/WebglRenderer.ts
index 3bf74242..fecd5742 100644
--- a/addons/xterm-addon-webgl/src/WebglRenderer.ts
+++ b/addons/xterm-addon-webgl/src/WebglRenderer.ts
@@ -94,7 +94,9 @@ export class WebglRenderer extends Disposable implements IRenderer {
   }
 
   public dispose(): void {
-    this._renderLayers.forEach(l => l.dispose());
+    for (const l of this._renderLayers) {
+      l.dispose();
+    }
     this._core.screenElement!.removeChild(this._canvas);
     super.dispose();
   }
@@ -106,10 +108,10 @@ export class WebglRenderer extends Disposable implements IRenderer {
   public setColors(colors: IColorSet): void {
     this._colors = colors;
     // Clear layers and force a full render
-    this._renderLayers.forEach(l => {
+    for (const l of this._renderLayers) {
       l.setColors(this._terminal, this._colors);
       l.reset(this._terminal);
-    });
+    }
 
     this._rectangleRenderer.setColors();
     this._glyphRenderer.setColors();
@@ -136,7 +138,9 @@ export class WebglRenderer extends Disposable implements IRenderer {
     this._model.resize(this._terminal.cols, this._terminal.rows);
 
     // Resize all render layers
-    this._renderLayers.forEach(l => l.resize(this._terminal, this.dimensions));
+    for (const l of this._renderLayers) {
+      l.resize(this._terminal, this.dimensions);
+    }
 
     // Resize the canvas
     this._canvas.width = this.dimensions.scaledCanvasWidth;
@@ -168,15 +172,21 @@ export class WebglRenderer extends Disposable implements IRenderer {
   }
 
   public onBlur(): void {
-    this._renderLayers.forEach(l => l.onBlur(this._terminal));
+    for (const l of this._renderLayers) {
+      l.onBlur(this._terminal);
+    }
   }
 
   public onFocus(): void {
-    this._renderLayers.forEach(l => l.onFocus(this._terminal));
+    for (const l of this._renderLayers) {
+      l.onFocus(this._terminal);
+    }
   }
 
   public onSelectionChanged(start: [number, number] | undefined, end: [number, number] | undefined, columnSelectMode: boolean): void {
-    this._renderLayers.forEach(l => l.onSelectionChanged(this._terminal, start, end, columnSelectMode));
+    for (const l of this._renderLayers) {
+      l.onSelectionChanged(this._terminal, start, end, columnSelectMode);
+    }
 
     this._updateSelectionModel(start, end, columnSelectMode);
 
@@ -184,11 +194,15 @@ export class WebglRenderer extends Disposable implements IRenderer {
   }
 
   public onCursorMove(): void {
-    this._renderLayers.forEach(l => l.onCursorMove(this._terminal));
+    for (const l of this._renderLayers) {
+      l.onCursorMove(this._terminal);
+    }
   }
 
   public onOptionsChanged(): void {
-    this._renderLayers.forEach(l => l.onOptionsChanged(this._terminal));
+    for (const l of this._renderLayers) {
+      l.onOptionsChanged(this._terminal);
+    }
     this._updateDimensions();
     this._refreshCharAtlas();
   }
@@ -222,7 +236,9 @@ export class WebglRenderer extends Disposable implements IRenderer {
   }
 
   public clear(): void {
-    this._renderLayers.forEach(l => l.reset(this._terminal));
+    for (const l of this._renderLayers) {
+      l.reset(this._terminal);
+    }
   }
 
   public registerCharacterJoiner(handler: (text: string) => [number, number][]): number {
@@ -245,7 +261,9 @@ export class WebglRenderer extends Disposable implements IRenderer {
     }
 
     // Update render layers
-    this._renderLayers.forEach(l => l.onGridChanged(this._terminal, start, end));
+    for (const l of this._renderLayers) {
+      l.onGridChanged(this._terminal, start, end);
+    }
 
     // Tell renderer the frame is beginning
     if (this._glyphRenderer.beginFrame()) {
diff --git a/addons/xterm-addon-webgl/test/WebglRenderer.api.ts b/addons/xterm-addon-webgl/test/WebglRenderer.api.ts
index 558605e2..e0aa68e7 100644
--- a/addons/xterm-addon-webgl/test/WebglRenderer.api.ts
+++ b/addons/xterm-addon-webgl/test/WebglRenderer.api.ts
@@ -18,7 +18,7 @@ const height = 600;
 
 describe('WebGL Renderer Integration Tests', async () => {
   const browserType = getBrowserType();
-  const isHeadless = process.argv.indexOf('--headless') !== -1;
+  const isHeadless = process.argv.includes('--headless');
   // Firefox works only in non-headless mode https://github.com/microsoft/playwright/issues/1032
   const areTestsEnabled = browserType.name() === 'chromium' || (browserType.name() === 'firefox' && !isHeadless);
   const itWebgl = areTestsEnabled ? it : it.skip;
@@ -893,7 +893,7 @@ async function getCellColor(col: number, row: number): Promise<number[]> {
 async function setupBrowser(options: ITerminalOptions = { rendererType: 'dom' }): Promise<void> {
   const browserType = getBrowserType();
   browser = await browserType.launch({
-    headless: process.argv.indexOf('--headless') !== -1
+    headless: process.argv.includes('--headless')
   });
   page = await (await browser.newContext()).newPage();
   await page.setViewportSize({ width, height });
diff --git a/src/browser/MouseZoneManager.ts b/src/browser/MouseZoneManager.ts
index 59b6b0f1..b6740157 100644
--- a/src/browser/MouseZoneManager.ts
+++ b/src/browser/MouseZoneManager.ts
@@ -156,9 +156,7 @@ export class MouseZoneManager extends Disposable implements IMouseZoneManager {
   private _onTooltip(e: MouseEvent): void {
     this._tooltipTimeout = undefined;
     const zone = this._findZoneEventAt(e);
-    if (zone && zone.tooltipCallback) {
-      zone.tooltipCallback(e);
-    }
+    zone?.tooltipCallback(e);
   }
 
   private _onMouseDown(e: MouseEvent): void {
diff --git a/src/browser/Terminal.ts b/src/browser/Terminal.ts
index b0964c21..686ae68d 100644
--- a/src/browser/Terminal.ts
+++ b/src/browser/Terminal.ts
@@ -162,11 +162,11 @@ export class Terminal extends CoreTerminal implements ITerminal {
   private _changeAnsiColor(event: IAnsiColorChangeEvent): void {
     if (!this._colorManager) { return; }
 
-    event.colors.forEach(ansiColor => {
+    for (const ansiColor of event.colors) {
       const color = rgba.toColor(ansiColor.red, ansiColor.green, ansiColor.blue);
 
       this._colorManager!.colors.ansi[ansiColor.colorIndex] = color;
-    });
+    }
 
     this._renderService?.setColors(this._colorManager!.colors);
     this.viewport?.onThemeChange(this._colorManager!.colors);
@@ -834,7 +834,7 @@ export class Terminal extends CoreTerminal implements ITerminal {
    * Change the cursor style for different selection modes
    */
   public updateCursorStyle(ev: KeyboardEvent): void {
-    if (this._selectionService && this._selectionService.shouldColumnSelect(ev)) {
+    if (this._selectionService?.shouldColumnSelect(ev)) {
       this.element!.classList.add('column-select');
     } else {
       this.element!.classList.remove('column-select');
diff --git a/src/common/CoreTerminal.ts b/src/common/CoreTerminal.ts
index c11554f1..384691ed 100644
--- a/src/common/CoreTerminal.ts
+++ b/src/common/CoreTerminal.ts
@@ -41,7 +41,7 @@ import { InputHandler } from 'common/InputHandler';
 import { WriteBuffer } from 'common/input/WriteBuffer';
 
 // Only trigger this warning a single time per session
-let hasWriteSyncWarnHappened: boolean = false;
+let hasWriteSyncWarnHappened = false;
 
 export abstract class CoreTerminal extends Disposable implements ICoreTerminal {
   protected readonly _instantiationService: IInstantiationService;
diff --git a/src/common/InputHandler.test.ts b/src/common/InputHandler.test.ts
index 0402f262..b5067193 100644
--- a/src/common/InputHandler.test.ts
+++ b/src/common/InputHandler.test.ts
@@ -1759,7 +1759,8 @@ describe('InputHandler', () => {
 
       assert.isNotNull(event);
       assert.deepEqual(event!.colors[0], { colorIndex: 19, red: 0xa1, green: 0xb2, blue: 0xc3 });
-    }),
+    });
+
     it('4: should ignore incorrect Ansi color change data', () => {
       // this is testing a private method
       assert.isNull(inputHandler.parseAnsiColorChange('17;rgb:a/b/c'));
@@ -1767,6 +1768,7 @@ describe('InputHandler', () => {
       assert.isNull(inputHandler.parseAnsiColorChange('17;rgba:aa/bb/cc'));
       assert.isNull(inputHandler.parseAnsiColorChange('rgb:aa/bb/cc'));
     });
+
     it('4: should parse a list of Ansi color changes', () => {
       // this is testing a private method
       const event = inputHandler.parseAnsiColorChange('19;rgb:a1/b2/c3;17;rgb:00/11/22;255;rgb:01/ef/2d');
diff --git a/src/common/InputHandler.ts b/src/common/InputHandler.ts
index a35f7981..13b0a0e7 100644
--- a/src/common/InputHandler.ts
+++ b/src/common/InputHandler.ts
@@ -2856,7 +2856,7 @@ export class InputHandler extends Disposable implements IInputHandler {
   protected _parseAnsiColorChange(data: string): IAnsiColorChangeEvent | null {
     const result: IAnsiColorChangeEvent = { colors: [] };
     // example data: 5;rgb:aa/bb/cc
-    const regex = /(\d+);rgb:([0-9a-f]{2})\/([0-9a-f]{2})\/([0-9a-f]{2})/gi;
+    const regex = /(\d+);rgb:([\da-f]{2})\/([\da-f]{2})\/([\da-f]{2})/gi;
     let match;
 
     while ((match = regex.exec(data)) !== null) {