By default, invoking a function like (function(){/*...*/})()
will set the value of this
in the function to window
(in a browser) irrespective of whatever the value of this
may be in the enclosing context where the function was created.
Using call
allows you to manually set the value of this
to whatever you want. In this case, it is setting it to whatever the value of this
is in the enclosing context.
Take this example:
var obj = {
foo:'bar'
};
(function() {
alert( this.foo ); // "bar"
}).call( obj );
You can see that we were able to manually set the value of this
to the object referenced by the obj
variable.