How Can I Access 'this' Correctly Inside JavaScript Callbacks?
This Affinity in JavaScript Callbacks
In JavaScript, utilizing instance methods within event handler callbacks can alter the scope of "this" from the intended instance to the source that invoked the callback. Consequently, code similar to the example below is often used:
function MyObject() {
this.doSomething = function() {
...
}
var self = this
$('#foobar').bind('click', function(){
self.doSomethng()
// this.doSomething() would not work here
})
}While functional, this approach may seem peculiar. Is there a more optimal solution?
Understanding Closure and "this" Affinity
This issue transcends jQuery and stems from JavaScript's handling of "this" and closures. Closures allow nested functions to access variables defined in the enclosing function, as illustrated below:
var abc = 1; // we want to use this variable in embedded functions
function xyz(){
console.log(abc); // it is available here!
function qwe(){
console.log(abc); // it is available here too!
}
...
};"This," however, behaves differently. Unlike ordinary variables that remain constant within a specific scope, "this" can vary dynamically across scopes.
// we want to use "this" variable in embedded functions
function xyz(){
// "this" is different here!
console.log(this); // not what we wanted!
function qwe(){
// "this" is different here too!
console.log(this); // not what we wanted!
}
...
};Solution: Aliasing "this"
To circumvent this challenge, JavaScript allows us to assign "this" to a variable, essentially aliasing it. This allows us to refer to the intended object throughout the nested functions.
var abc = this; // we want to use this variable in embedded functions
function xyz(){
// "this" is different here! --- but we don't care!
console.log(abc); // now it is the right object!
function qwe(){
// "this" is different here too! --- but we don't care!
console.log(abc); // it is the right object here too!
}
...
};This same principle applies to other pseudo variables such as "arguments."
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