How to use the javascript call method in jQuery?

Question

Is it possible to use the call method of javascript (as described in the [mdn documentation]) in order to pass the argument this?

Having for example this code:

console.log(this);
$('#image_id').load(function () {
    console.log(this);
});

I want that the second this (the one included in the load function) refers to the same as the first one.

I've tried with

console.log(this);
$('#image_id').load.call(this, function () {
    console.log(this);
});

But it doesn't work.

Thank you all in advance for any suggestion.

Answer 1

Not like that, because you're not calling the callback. It's being called internally.

You could use .bind though.

console.log(this);
$('#image_id').load( function () {
    console.log(this);
}.bind(this));

But it isn't available in older browsers. (This is native .bind(), not jQuery's.)

---

jQuery has something that will work called $.proxy...

console.log(this);
$('#image_id').load($.proxy(function () {
    console.log(this);
},this));

...where the first argument is your function, and the second argument is the value you want to use for this in the callback.

Answer 2

You don't need call (or apply)

You should do this instead:

var that = this;
console.log(this);
$('#image_id').load( function () { 
    console.log(that); 
});

Javascript has lexical scoping, which means that the variable that is available to your callback, and has the value of where it is defined. In this case, that is defined to be this in the outer scope.

Answer 3

Yes you can .call jQuerys function with whatever, but that only affects that function. The function you pass is a separate callback function with this controlled by jQuery.

You can use $.proxy to force a context of the callback.

$('#image_id').bind( "load", $.proxy( console.log, console, this ) );

If you wish to do more than logging it becomes more ugly:

$('#image_id').bind( "load", $.proxy( function(){
     console.log( this );
     alert( this );
}, this ) );

Answer 4

var self = this;
$('#image_id').load(function(){
    (function(){
        console.log(this);
    }).call(self);
});