如何在极简主义条件声明中获得更好的表现？

Question

I work with JavaScript but I always wonder this for all the languages.

Do I get better performance doing this:

var i = 0;
if(j < 0) 
{
   i = 1;
}

Or this?

var i;
if(j < 0) 
{
    i = 1;
}
else 
{
    i = 0;
}

With 50% chance to have j < 0

Answer 1

That will depend on the implementation of javascript engine, which, at least if you write your code for the Web, is out of your control.

One browser might be faster with first version of the code, the other with the second version. And tomorrow it might change.

Do not optimize things like this unless you have pinned down this one line of code as a bottleneck of your task.

You might want to read when to optimize .

You will be better of to write readable and well designed code, and let the browser vendors wory about machine level optimisations.

The things you should optimize are algorithms, and not language specific constructions.

Answer 2

Neither of your code makes much of a difference. Depends on the JS engine of course but todays engines are pretty advanced and optimize code very well(especially V8 on chrome and node.js).

Benchmark it. You can use simple console.time('label'); console.timeEnd('label') console.time('label'); console.timeEnd('label') at least in Chrome.

In my opinion your code looks ugly and like a bloat. A lot of space is consumed with no content. I would prefer this approach as it reads much faster and you should care about readability as much as performance :

var i;    
if(j < 0) {
    i = 1;
} else {
    i = 0;
}

Also you have an access to ternary operator:

var i = j < 0 ? 1 : 0;

which is readable if you do not nest it. Again - performance wise all of them are equal and will differt by maybe a millisecond or two so you should not care about performance in such simple cases. Care about readability :)

Also performance will depend on your j value. If optimizer will see that you set j to 1 . It will short-circuit the whole code and simply set i = 0 . IMHO in such simple cases it's not useful to spend time to search for improvement except for readability :).