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javascriptcallsettimeoutapply
Manish Kumar
Manish Kumar

Reputation: 548

why can't we do call and apply on setTimeout?

Why can't we do call and apply on setTimeout,

var obj={}
window.setTimeout.call(obj,callback,delay);//it throws error stating illegal invocation

Upvotes: 3

Views: 3080

Answers (2)

Scott Marcus
Scott Marcus

Reputation: 65815

It makes no sense to use .call on setTimeout since .call is meant to invoke a function and supply context to that function when it is invoked. In other words, you're not trying to invoke setTimeout with context supplied to it, you're trying to invoke the callback with context supplied to it.

To accomplish this with setTimeout, you'd use .bind, as in: 

 var obj={};
 window.setTimeout(callback.bind(obj),delay);

Upvotes: 3

gnerkus
gnerkus

Reputation: 12027

From the WHATWG setTimeout documentation:

The setTimeout() method must return the value returned by the timer initialisation steps, passing them the method's arguments, the object on which the method for which the algorithm is running is implemented (a Window or WorkerGlobalScope object) as the method context, and the repeat flag set to false.

setTimeout needs to be called from the context of the window object. The context passed into the .call method is not the window object. To call setTimeout correctly, do:

setTimeout.call(window, callback, delay);

Upvotes: 2

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