Summary of for loop performance optimization in JS

This article introduces to you a summary of for loop performance optimization in JS. It has certain reference value. Friends in need can refer to it. I hope it will be helpful to you.

We really use too many FOR loops, but have you paid attention to its optimized writing? Record:

1. The most common way of writing, there is nothing wrong with it

for (var i = 0; i < 10; i++) {    // do something...}

2. The number of loops is variable Situation

for (var i = 0; i < arr.length; i++) {    // do something...}

In fact, most people write this way. The disadvantage of this way of writing is that the array must be read every time it loops The length is not cost-effective

3. Optimized writing of variables

for (var i = 0, l = arr.length; i < l; i++) {    // do something...}

Store the length and then loop No need to read the length

4. The above 3 can also be written like this

var i = 0, l = arr.length;        
for (; i < l; i++) {    // do something...}

This is just 3 It's just a variation of, another way of writing, not optimization at all. Because there is no block-level scope, the effect is the same as 3

5. Optimized writing and upgraded version

for (var i = arr.length - 1; i >= 0; i--) {    // do something...}

Recommended writing method, which saves a variable based on the third method.

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