JavaScript | Angular | Controller As Syntax: Cannot Use `this`

Question

Cannot Use ControllerAs this

Can anyone explain the following scenario to me, please?

Works

ng-controller="Parent as thus"

Breaks

ng-controller="Parent as this"

That single letter which makes it a keyword -- which I want -- wrecks the forest.

Why is this?

P.S. I'm aware of the vm convention, but I find it disturbs portability of controllers/viewmodels.

Answer 1

The problem is certainly not that this is a reserved word in JavaScript. There is no rule in the controller as syntax that says you would need to assign the value of this to a variable with the same name as the controller and I'm pertty sure angular won't do such thing either. Why would it? That would be incredibly stupid use of Function constructor and just a needless bug.

There's a simple way to test that JavaScript reserved words are not the issue here. Name your controller "throw". "Parent as throw". throw is a reserved word, but does that throw errors? No. Does that work? Yes.

this is, however, reserved in the context of angular's own template expressions. It's used to refer to the current scope of the expression.

<div ng-controller="Parent as this">
    {{log(this)}}
</div>


angular.module('testApp', []).controller('Parent', function($scope){
    this.test = 'foo';
    $scope.log = function(arg){
        console.log(arg);
    };
});

The above won't throw errors, but it won't log the controller either. Instead, it will log a scope object containing the log function and $parent and what not.

In fact, it will also contain something intresting to us: property this: Object, our controller.

And sure enough, change the template expression to {{log(this.this)}} and it will log the controller instance just fine. Still wouldn't use 'this' as the name though, it would probably just cause more bugs by mistake than undefined functions ever have.

Answer 2

You are cannot use this as the instance name. this is a reserved keyword.

It would be the equivalent of doing:

var this = new Controller();

You can see that is wrong. It should be something like:

var ctrl = new Controller();

This is essentially what angularJs does behind the scenes when you do controllerAs="Controller as ctrl"