In case you wonder why this
changes even though you clearly bound it to be MyClass
before, that's because you use call
with dummy_obj
on the spy.
The spy wraps the original function, so it has no concept of that function's binding. It will still accept a different binding on the wrapper function, then try to call the original with that this
, which is then ignored by the original function.
var context = {foo: 'bar'};
var original = _.bind(function () { console.log(this); }, context);
var spy = function (original) {
var spyFn = function () {
var _this = this;
spyFn.calledOn = function (ctx) { return ctx === _this; };
return original.apply(this, arguments);
};
return spyFn;
};
var originalSpy = spy(original);
// Will call the spyFn with a different `this`, but will not affect the original binding
originalSpy.call({something: 'else'});
>> {foo: 'bar'}
// Since the spy cannot know the original binding, it will think the assumption is false.
originalSpy.calledOn(context) === false;