Javascript - how do i set the 'this' variable for a function

Question

I have a function which takes a callback function. How can I set the 'this' variable of the callback function?

eg.

function(fn){
    //do some stuff
    fn(); //call fn, but the 'this' var is set to window
    //, how do I set it to something else
}

Answer 1

you can execute a function in the context of an object using call:

fn.call( obj, 'param' )

There's also apply

Only difference is the syntax for feeding arguments.

Answer 2

You can use either apply() or call().

Either allows you to execute a function with your choice of what this is inside the function. Apply takes the arguments for the function as an array, while call allows you to specify them individually.

Answer 3

funct.call(objThatWillBeThis, arg1, ..., argN);

or

funct.apply(objThatWillBeThis, arrayOfArgs);

Answer 4

You can use either .call() or .apply(). Depending on your requirement. Here is an article about them.

Basically you want:

function(fn){
    //do some stuff
    fn.call( whateverToSetThisTo ); //call fn, 

}