Assign object[key] to a temp variable in a javascript “for…in” loop?

Question

I'm working on a JS to show different messages depending on the current url's hash. Now, that's all working, but I was wondering what the best way would be to access my messages (They'll be coded into a .js file)

At the moment, I have the messages stored in a object like this:

popups = {
    TemplateMessage: {
        title: "Template Popup Title", 
        message: "This is a template popup message! Copy this to add a message.",
        modal: true
    },
    AnotherMessage: {
        title: "another title", 
        message: "message.",
        modal: true
    } /* etc */
};

the way I'm accessing these messages is with a "for in: loop, as follows:

for (key in popups) {
    //Do something with...
    popups[key].title;
    popups[key].message;
    popups[key].modal;
}

But would it be more efficient to assign popups[key] to a temporary variable? Like:

var p;
for (key in popups) {
    p = popups[key];
    //Do something with...
    p.title;
    p.message;
    p.modal;
}

This is all relatively small-scale at the moment and it wouldn't matter a lot (if anything at all) at this stage, but what if you have, say, 25 different objects with 50 properties on each of them? I guess my real question would be, is there a (relatively) significant difference in obtaining a variable from a temp variable, or from a object in a object?

I'm not quite sure how to properly test this, any suggestions?

Answer 1

It turns out it is indeed faster to assign your object[key] to a temporary variable in for-in loops with large objects, as seen in this jsPerf test. That way, you won't have to obtain object[key] for every property of the object.