add missing api docs and refactor serialize implementation by using list join instead and some code clean up

addons/xterm-addon-serialize/src/SerializeAddon.ts

@@ -15,28 +15,21 @@ export class SerializeAddon implements ITerminalAddon {
   }
 
   public serialize(rows?: number): string {
+    // TODO: Add frontground/background color support later
     if (!this._terminal) {
-      return '';
+      throw new Error('No terminal found!');
     }
     const buffer = this._terminal.buffer;
     const length = Math.max(0, Math.min((rows === undefined ? buffer.length : rows), buffer.length));
-    let data = '';
+    const lines: string[] = new Array<string>(length);
 
     for (let i = 0; i < length; i++) {
       const line = buffer.getLine(i);
-      const last = i === length - 1;
-      if (line) {
-        data += line.translateToString();
-      }
-      if (!last) {
-        data += '\r\n';
-      }
+      lines[i] = line ? line.translateToString() : '';
     }
 
-    return data;
+    return lines.join('\r\n');
   }
 
-  public dispose(): void {
-    if (this._terminal !== undefined) { }
-  }
+  public dispose(): void { }
 }

addons/xterm-addon-serialize/typings/xterm-addon-serialize.d.ts

@@ -20,6 +20,14 @@ declare module 'xterm-addon-serialize' {
      */
     public activate(terminal: Terminal): void;
 
+    /**
+     * Serializes terminal rows into a string that can be written back to the terminal
+     * to restore the state. The cursor will also be positioned to the correct cell.
+     * When restoring a terminal it is best to do before `Terminal.open` is called
+     * to avoid wasting CPU cycles rendering incomplete frames.
+     * @param rows The number of rows to serialize, starting from the top of the
+     * terminal. This defaults to the number of rows in the viewport.
+     */
     public serialize(rows?: number): string;
 
     /**