Question

If you are doing something like the following:

var i = $('input[@name=some_field]'); if (i.val() != '' && !(i.val() >=1 && i.val() <= 36) || i.val() == 'OT')) {      i.focus(); } 

is i.val() fast enough to use it multiple times or should you do:

var value = i.val(); 

first and then use value in the if statement, like:

var i = $('input[@name=some_field]'); var value = i.val(); if (value != '' && !(value >=1 && value <= 36) || value == 'OT')) {      i.focus(); } 

…?

Answer 1

This isn’t necessarily a jQuery question but it applies pretty well to most programming languages. And in fact, there’s a lot more to this question than just performance issues.

One thing to keep in mind is that if you store the value, then there is no possibility that it will change during the execution of your subsequent code. Most of the time, this is what you expect and want. But it is also possible in some circumstances that the call to val() will return a different value, especially if you are looping and doing something that takes any significant time.

In your particular example, the chances of this occurring are pretty low because it’s only a few calls and not in a looping construct. Given that there are only a few calls, performance likely won’t be a major concern here. But the theory of the point remains – if you want to guarantee that the value doesn’t change, put it in a variable. Since it also gives you the best of the performance considerations, I think this would be a best practice in most cases.