Is not having local functions a micro optimisation?

Question

Would moving the inner function outside of this one so that its not created everytime the function is called be a micro-optimisation?

In this particular case the doMoreStuff function is only used inside doStuff. Should I worry about having local functions like these?

function doStuff() {
    var doMoreStuff = function(val) {
         // do some stuff
    }

    // do something
    for (var i = 0; i < list.length; i++) {
         doMoreStuff(list[i]);
         for (var  j = 0; j < list[i].children.length; j++) {
              doMoreStuff(list[i].children[j]);
         }
    }
    // do some other stuff

}

An actaul example would be say :

function sendDataToServer(data) {
    var callback = function(incoming) {
         // handle incoming
    }

    ajaxCall("url", data, callback);

} 

Answer 1

Not sure if this falls under the category "micro-optimization". I would say no.

But it depends on how often you call doStuff. If you call it often, then creating the function over and over again is just unnecessary and will definitely add overhead.

If you don't want to have the "helper function" in global scope but avoid recreating it, you can wrap it like so:

var doStuff = (function() {
    var doMoreStuff = function(val) {
         // do some stuff
    }
    return function() {
        // do something
        for (var i = 0; i < list.length; i++) {
            doMoreStuff(list[i]);
        }
        // do some other stuff 
    }
}());

As the function which is returned is a closure, it has access to doMoreStuff. Note that the outer function is immediately executed ( (function(){...}()) ).

Or you create an object that holds references to the functions:

var stuff = {
    doMoreStuff: function() {...},
    doStuff: function() {...}
};

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More information about encapsulation, object creation patterns and other concepts can be found in the book JavaScript Patterns.