Question

This may be a bit abstract but I’m trying to get my head round JavaScript closures etc. Take the following code:

function MyObj() {
    var me = this;

    this.foo = function(bar) {
        // Do something with 'bar'
    }

    // Set up lots of local variables etc.
    // ....

    $(window).load(function() {
        // Add a delegated click handler to specific <input> elements
        $(document).on('click.myobj', 'input.special', function() {
            // Do something with the <input> that triggered the click event
            me.foo(this);
        });
    });
}

var myObj = new MyObj();

The anonymous function passed to that is bound to the click event creates a closure that references me. What I want to know is whether it’s better to do something like this instead (to avoid the closure):

$(window).load(function() {
    // Add a delegated click handler to specific <input> elements
    (function(localMe) {
        $(document).on('click.myobj', 'input.special', function() {
            // Do something with the <input> that triggered the click event
            localMe.foo(this);
        });
    })(me);
});

Is this a better approach, or am I being overly paranoid about creating a closure? Alternatively, is there a “third way”?

---

EDIT

Additionally, would it be better to do something like this:

$(window).load(function() {
    // Add a delegated click handler to specific <input> elements
    $(document).on('click.myobj', 'input.special', {localMe : me}, function(event) {
        // Do something with the <input> that triggered the click event
        event.data.localMe.foo(this);
    });
});

Answer 1

The latter is (AFAIK) more efficient, but probably not measurably so unless used in a tight loop.

The reason is that all variable dereferencing must follow the scope chain. In the latter case, the variable localMe can be found in the anonymous function’s parameter list.

In the former case, the variable isn’t found there, but in the outer scope. This traversal up the scope chain takes extra time.