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I've heard this quite a few times. Are JavaScript loops really faster when counting backward? If so, why? I've seen a few test suite examples showing that reversed loops are quicker, but I can't find any explanation as to why!
I'm assuming it's because the loop no longer has to evaluate a property each time it checks to see if it's finished and it just checks against the final numeric value.
I.e.
for (var i = count - 1; i >= 0; i--) { // count is only evaluated once and then the comparison is always on 0. } 
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Why is ++i faster than i++ in C++? I've heard this question come up a few times in C++ programming circles, “Why is ++i faster/better than i++?” The short answer is: i++ has to make a copy of the object and ++i does not. The long answer involves some code examples.
According to the Google C++ Style Guide, "when the return value is ignored, the 'pre' form ( ++i ) is never less efficient than the 'post' form ( i++ ), and is often more efficient."
No there will be no difference at all.
Increment is always faster than decrement.
It's not that i-- is faster than i++. Actually, they're both equally fast.
What takes time in ascending loops is evaluating, for each i, the size of your array. In this loop:
for(var i = array.length; i--;) You evaluate .length only once, when you declare i, whereas for this loop
for(var i = 1; i <= array.length; i++) you evaluate .length each time you increment i, when you check if i <= array.length.
In most cases you shouldn't even worry about this kind of optimization.
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