How to pass context to anonymous function?

Question

There are some function, thats do something long work and its provides callback.

someFunc: function(argument, callback, context) {   // do something long    // call callback function   callback(context); } 

In application I use this function

someFunc('bla-bla', function (context) {   // do something with this scope   context.anotherFunc(); }, this); 

How to implement callback function without passing context parameter?

Need some like this:

someFunc('bla-bla', function () {   // do something with this scope   this.anotherFunc(); }, this); 

Answer 1

The accepted answer seems somewhat outdated. Assuming you're operating on a relatively modern browser, you can use Function.prototype.bind in vanilla javascript. Alternatively, if you are using underscore or jQuery, you can use _.bind or $.proxy respectively (which will fallback to call/apply if necessary).

Here is a simple demonstration of these three options:

// simple function that takes another function // as its parameter and then executes it. function execute_param(func) {     func(); }  // dummy object. providing an alternative context. obj = {}; obj.data = 10;  // no context provided // outputs 'Window' execute_param(function(){     console.log(this); });  // context provided by js - Function.prototype.bind // src: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function/bind // outputs 'Object { data=10 }'' execute_param(function(){     console.log(this); }.bind(obj));  // context provided by underscore - _.bind // src: http://underscorejs.org/#bind // outputs 'Object { data=10 }' execute_param(_.bind(function(){     console.log(this); },obj));  // context provided by jQuery - $.proxy // src: http://api.jquery.com/jQuery.proxy/ // outputs 'Object { data=10 }' execute_param($.proxy(function(){     console.log(this); },obj)); 

You can find the code in a jsfiddle here: http://jsfiddle.net/yMm6t/1/ (note: ensure that the developer console is open, or you won't see any output)