How do I access `this` from JavaScript via JS - Dart interop?

The Callback constructor can pass the this from JavaScript. According to the API docs for Callback:

new Callback.many(Function f, {bool withThis: false})new Callback.once(Function f, {bool withThis: false})

Here is an example:

Dart code:

import 'dart:html';import 'package:js/js.dart' as js;void main() {  var greeter = js.context['greeter'];  var msg = greeter['greet']('Bob');  greeter['doCoolStuff'] = new js.Callback.many(doCoolStuff, withThis: true);}doCoolStuff(jsThis) {  print(jsThis['msg']);}

Notice the use of withThis: true when creating the Callback. The this from JavaScript is passed in as the first argument to the callback function. In this case, I give it a name of jsThis.

JavaScript code:

function Greeter() {  this.msg = 'hello';  var that = this;  document.getElementById('clickme').addEventListener('click', function() {    that.doCoolStuff();  });}Greeter.prototype.greet = function(name) {  return this.msg + ' ' + name;}var greeter = new Greeter();document.getElementById('clickme').addEventListener('click', function() {  greeter.doCoolStuff(); // comes from Dart land});