Javascript performance: Variable vs Large object's attribute

Question

I am building a number of HTML5 games and I am not sure about one thing in javascript.

When dealing with a large object (with a lot of attributes and methods), is it somehow different, if I store the attribute value in a variable?

Say I have to check for some value in application.data.setings.foo.bar multiple times per second. Should I store it in a variable fooBar? If I understand it correctly, the variable would be just a reference, so it shouldn't matter.

so: Should you store values of large objects' attributes in variables?

Answer 1

This diagram give you your answer. http://oreilly.com/server-administration/excerpts/even-faster-websites/writing-efficient-javascript.html#access_times_for_object_properties_by_de

Answer 2

I believe what you are asking is:

If you have a variable called:

application.data.settings.foo.bar = { some: 'value' }

Is it more performant to access it by using application.data.settings.foo.bar - or to instead say: var bar = application.data.settings.foo.bar and then refer to bar.

My guess is that the assignment to variable is probably slightly more performant - simply because there are less steps for the interpreter to take in order to access the relevant item. If you use application.data.settings.foo.bar - the interpreter has to utilize the reference to the application object, then reference it's data property, then reference its setting property, then reference its foo property, then reference its bar property. This is 5 steps.

If you reference it into a local variable for access - you are still hitting the same object, but you are hitting it directly on each reference.

At the end of the day, however, this is unlikely to be a performance enhancement which is hugely noticeable, unless you are doing a lot of heavy, rapid-access looping or something similar.

Answer 3

For numbers you may see a performance improvement if you place it in a variable