Home » Using var self = this or .bind(this)? [closed]

Using var self = this or .bind(this)? [closed]


Things that would favor var self = this;

  • bind isn’t supported in IE8 and Safari5. If you aim to build a library or code that supports legacy browsers, then var self = this would be more cross-browser friendly.

  • Sometimes, callbacks are bound to a certain context when executed like in the case of jQuery’s $.each where this is the current item. If you don’t want to lose this context but still want to have the parent context, then it’s another reason to use var self = this;.

  • Calling bind creates a brand new function with a forced context. This function creation step might be a performance issue in the large scale especially if you call bind inside a loop.

Reasons that would favor bind

  • Performance wouldn’t be an issue if you just created a bound function once and reused it in several places. Like you can create a bound function and call that bound function in a loop (instead of calling bind in a loop).

  • bind also alleviates you from doing call(customContext) or apply(customContext) explicitly all the time.

  • Scope lookup (looking for variables if not found in the current scope) can pose a performance problem especially in very deep scopes. You’ve probably heard of the tip “passing to local is better”.

I’m not saying bind is bad (I use them extensively myself). It just needs to be used in the right situations. Also, the performance issues for both might be so negligible, they can only be seen if you aim to do stuff in less than 16ms (do stuff in 60fps).

Just to add another alternative, instead of doing

var self = this;
something( function () {
    // callback stuff
} );

one can also do this:

( function( self ) {
    something( function () {
        // callback stuff
    } );
} )( this );

Is it better? It might depend. The downsides are another scope and a deeper level of indentation.

One upside is that it’s self-contained and the new scope avoids cluttering up the surriounding scope, though you can argue that in well-designed code there shouldn’t be too much code in one scope anyway.

One could also say it’s not too readable, though I personally would argue that bind( this ) really is that much more readable.

I just wanted to point out another option as having more options to choose from is generally a good thing.

Simple rule of thumb use bind if you don’t need to have a reference to the original this context. If the original this context is needed use a self variable obviously.

    url: '../Component/GetSearchFilters',
    success: function (response) {
        console.log("Outer scope:", this);


var me = this;
    url: '../Component/GetSearchFilters',
    success: function (response) {
        console.log("Outer scope:", me);

Using bind is slightly more consise and easier to read than the me variable but one way over the other really isn’t a big deal.

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