Mac OSX: altIsMeta support

* Support for altIsMeta option
* Instead of providing third-level shift characters
* Sample demo application using new altIsMeta option

demo/main.js

@@ -87,6 +87,7 @@ function createTerminal() {
     terminalContainer.removeChild(terminalContainer.children[0]);
   }
   term = new Terminal({
+    altIsMeta: true,
     cursorBlink: optionElements.cursorBlink.checked,
     scrollback: parseInt(optionElements.scrollback.value, 10),
     tabStopWidth: parseInt(optionElements.tabstopwidth.value, 10)

src/Interfaces.ts

@@ -128,6 +128,7 @@ export interface IInputHandlingTerminal extends IEventEmitter {
 }
 
 export interface ITerminalOptions {
+  altIsMeta?: boolean;
   bellSound?: string;
   bellStyle?: string;
   cancelEvents?: boolean;

src/Terminal.test.ts

@@ -503,6 +503,9 @@ describe('term.js addons', () => {
       it('should return \\x1b[5C for alt+right', () => {
         assert.equal(term.evaluateKeyEscapeSequence({ altKey: true, keyCode: 39 }).key, '\x1b[1;5C'); // CSI 5 C
       });
+      it('should return \\x1ba for alt+a', () => {
+        assert.equal(term.evaluateKeyEscapeSequence({ altKey: true, keyCode: 65 }).key, '\x1ba');
+      });
     });
 
     describe('On macOS platforms', () => {
@@ -515,6 +518,19 @@ describe('term.js addons', () => {
       it('should return \\x1bf for alt+right', () => {
         assert.equal(term.evaluateKeyEscapeSequence({ altKey: true, keyCode: 39 }).key, '\x1bf'); // CSI 5 C
       });
+      it('should return undefined for alt+a', () => {
+        assert.strictEqual(term.evaluateKeyEscapeSequence({ altKey: true, keyCode: 65 }).key, undefined);
+      });
+    });
+
+    describe('with altIsMeta', () => {
+      beforeEach(() => {
+        term.browser.isMac = true;
+        term.setOption('altIsMeta', true);
+      });
+      it('should return \\x1ba for alt+a', () => {
+        assert.equal(term.evaluateKeyEscapeSequence({ altKey: true, keyCode: 65 }).key, '\x1ba');
+      });
     });
 
     it('should return \\x1b[5A for alt+up', () => {
@@ -597,6 +613,22 @@ describe('term.js addons', () => {
       };
     });
 
+    describe('with altIsMeta', () => {
+      beforeEach(() => {
+        term.browser.isMac = true;
+        term.setOption('altIsMeta', true);
+      });
+
+      it('should interfere with the alt key on keyDown', () => {
+        evKeyDown.altKey = true;
+        evKeyDown.keyCode = 81;
+        assert.equal(term.keyDown(evKeyDown), false);
+        evKeyDown.altKey = true;
+        evKeyDown.keyCode = 192;
+        assert.equal(term.keyDown(evKeyDown), false);
+      });
+    });
+
     describe('On Mac OS', () => {
       beforeEach(() => {
         term.browser.isMac = true;

src/Terminal.ts

@@ -80,6 +80,7 @@ const DEFAULT_OPTIONS: ITerminalOptions = {
   scrollback: 1000,
   screenKeys: false,
   debug: false,
+  altIsMeta: false,
   cancelEvents: false,
   disableStdin: false,
   useFlowControl: false,
@@ -1373,7 +1374,7 @@ export class Terminal extends EventEmitter implements ITerminal, IInputHandlingT
       return this.cancel(ev, true);
     }
 
-    if (isThirdLevelShift(this.browser, ev)) {
+    if (!this.options.altIsMeta && isThirdLevelShift(this.browser, ev)) {
       return true;
     }
 
@@ -1698,8 +1699,8 @@ export class Terminal extends EventEmitter implements ITerminal, IInputHandlingT
             // ^] - Operating System Command (OSC)
             result.key = String.fromCharCode(29);
           }
-        } else if (!this.browser.isMac && ev.altKey && !ev.ctrlKey && !ev.metaKey) {
-          // On Mac this is a third level shift. Use <Esc> instead.
+        } else if ((!this.browser.isMac || this.options.altIsMeta) && ev.altKey && !ev.ctrlKey && !ev.metaKey) {
+          // On Mac this is a third level shift. Use <Esc> instead if !altIsMeta
           if (ev.keyCode >= 65 && ev.keyCode <= 90) {
             result.key = C0.ESC + String.fromCharCode(ev.keyCode + 32);
           } else if (ev.keyCode === 192) {