When updating some of the elements in an object array in Javascript, which one is a more efficient way considering the array size?

Question

Consider this very simple js code below:

for(var i = 0; i < rows.length; i++) {
 if(rows[i].index !== i) {
 rows[i].index = i;
 }
}

Say, the length of the array is 8, and it will enter the if block 2 times. Is it better to do this way:

for(var i = 0; i < rows.length; i++) {
 rows[i].index = i;
}

I want to know which one is less costly with large arrays and small arrays; the if block, or the value assign in every cycle of the loop?

• maioman: I would say the version without the if , but you should test it on jsperf
• Bergi: There's only one way to find out: measure it. But you should not care, and go for the simpler one.

Answer 1

it shouldn't really matter. I still tried it on jsPerf for the sake of curiousity and it seems that the second version is faster.