How to use the javascript call method in jQuery?
-
17-04-2021 - |
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.
Solution
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.
OTHER TIPS
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.
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 ) );
var self = this;
$('#image_id').load(function(){
(function(){
console.log(this);
}).call(self);
});