Is there a specific advantage to iterating through arrays backwards in JavaScript?

Is it common practice in Javascript to use the following loop:

for (var i = array.Length - 1; i >= 0; i--) { /* do something here */ };

I haven't seen this in other languages. Are there any advantages to this compared to:

for (var i = 0; i < array.Length; i++) { /* do something here */ };

The only benefit I can think of is caching the array length in the first option, which may not significantly improve performance. Another approach could be:

var top =  array.Length;
for (var i = 0; i < top; i++) { /* do something here */ };    

This provides the same caching benefit, but may be slightly less performant if you are trying to minimize your code (saving around 8 characters when minifying the script).

Answer №1

At times, the impact can be significant.

let items = container.elements, count = items.length, index;
for( index=0; index<count; index++) container.removeChild(items[index]);
// ^ LEADS TO ERROR (unless count is 0 or 1)

for( index=count-1; index>=0; index--) container.removeChild(items[index]);
// ^ successful

Answer №2

One strategy that has been pointed out by others is that moving backwards can simplify the process of removing elements from an array. Additionally, this approach may offer a slight performance advantage, as demonstrated in a performance test (jsperf). It is believed that starting at the end and progressing towards the beginning may be faster because there is no need to retrieve the array's length property after each loop iteration.

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