Add a JavaScript REPL example (that works with terminals).

examples/js/repl.js

Index: examples/js/repl.js
diff --git a/examples/js/repl.js b/examples/js/repl.js
new file mode 100644
index 0000000000000000000000000000000000000000..18e8c936b4c143f1c19ffdef1861b300e45329cc
--- /dev/null
+++ b/examples/js/repl.js
@@ -0,0 +1,112 @@
+#!mojo mojo:js_content_handler
+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Simple JavaScript REPL example, using TerminalClient.
+//
+// To run this, do something like:
+//
+//   $ sky/tools/skydb start out/Debug mojo:moterm_example_app
+//
+// At the moterm_example_app prompt:
+//
+//   :) file:///absolute/path/to/repl.js
+//
+// Then, at the repl.js prompt, enter JavaScript, e.g.:
+//
+//   > 1 + 2
+//   3
+//   > function f(x, y) { return x + y; }
+//   undefined
+//   > f("abc", 123)
+//   "abc123"
+//
+// (Note that multiple simultaneous REPLs will share the same global state, that
+// the global state will persist, etc. This is really just intended as a demo!)
+
+define("main", [
+  "mojo/services/public/js/application",
+  "mojo/services/files/public/interfaces/types.mojom",
+  "mojo/services/terminal/public/interfaces/terminal_client.mojom",
+], function(application, files_types, terminal_client) {
+  const Application = application.Application;
+  const TerminalClient = terminal_client.TerminalClient;
+  const Whence = files_types.Whence;
+
+  function stringToBytes(s) {
+    return s.split("").map(function (c) { return c.charCodeAt(0); });
+  }
+
+  class Repl {
+    constructor(terminal) {
+      this.terminal_ = terminal;
+    }
+
+    start() {
+      // TODO(vtl): Handle errors.
+      var self = this;
+      this.terminal_.write(stringToBytes("> "), 0, Whence.FROM_CURRENT)
+          .then(function (result) { self.didWritePrompt_(result); });
+    }
+
+    didWritePrompt_(result) {
+      // TODO(vtl): Handle errors.
+      var self = this;
+      this.terminal_.read(1000, 0, Whence.FROM_CURRENT)
+          .then(function (result) { self.didRead_(result); });
+    }
+
+    didRead_(result) {
+      // TODO(vtl): Handle errors.
+      var s = String.fromCharCode.apply(String, result.bytes_read).trim();
+      var r;
+      try {
+        // Note: Indirectly calling eval as follows leads to the evaluation
+        // working at global scope (as of ECMAScript 5). (This allows us to
+        // persist state across evals without doing any work.)
+        var geval = eval;
+        r = geval(s);
+      } catch (e) {
+        r = e;
+      }
+      var resultString;
+      if (typeof(r) == "string") {
+        resultString = "\"" + r + "\"";
+      } else if (r === null) {
+        resultString = "null";

[hansmuller, 2015/05/12 22:33:01]

I suppose you could deal with the other cases with:

try {
  resultString = "" + r;
} catch (e) {
   resultString = "Oops";
}

[viettrungluu, 2015/05/12 22:52:25]

Oh, good point. (Silly JavaScript. I forgot that "" + r isn't the same as
"".toString().)

Also, I moved the try { ... } around all the cases, in case something like "" +
r fails somehow.

And I also "fixed" the handling for arrays. (Array.isArray() is a class method,
added to ECMAScript 5.)

+      } else if (r === undefined) {
+        resultString = "undefined";
+      } else {
+        try {
+          resultString = r.toString();
+        } catch (e) {
+          resultString = "Oops!";
+        }
+      }
+      var self = this;
+      this.terminal_.write(stringToBytes(resultString + "\n"), 0,
+                           Whence.FROM_CURRENT)
+          .then(function (result) { self.didWriteResult_(result); });
+    }
+
+    didWriteResult_(result) {
+      this.start();
+    }
+  }
+
+  class TerminalClientImpl {
+    connectToTerminal(terminal) {
+      (new Repl(terminal)).start();
+    }
+  }
+
+  class ReplApp extends Application {
+    acceptConnection(initiatorURL, initiatorServiceExchange) {
+      initiatorServiceExchange.provideService(TerminalClient,
+                                              TerminalClientImpl);
+    }
+  }
+
+  return ReplApp;
+});