What does 'var vm = this;' mean in angular controllers?

Question

I was browsing some stuff on github and I saw inside controller.js, someone had put the following:

function ImageController ($scope, $timeout) {
   var vm = this;
}

What is this used for?

Answer 1

The vm in this case means viewmodel.

It is a shortcut, so instead of writing this.someMethod() you can use vm.someMethod().

Very common when you use Controller As syntax, so you don´t use the $scope by "accident".

Also, the this keyword can be messy to use, since it may reference different things depending on where it is used.

Answer 2

Why?: Helps avoid the temptation of using $scope methods inside a controller when it may otherwise be better to avoid them or move the method to a factory, and reference them from the controller.

you can check full John Papa Angular Style to learn deeper...