后增量与预增量 - Javascript优化 [英] post increment vs pre increment - Javascript Optimization

问题描述

当我偶然发现这个名为JSpeed的项目 - Javascript优化时，我正在浏览Google Code。

I was browsing Google Code when I chanced upon this project called JSpeed - optimization for Javascript.

我注意到其中一项优化是更改 i ++ 到 ++ i in for for return语句。

I noticed one of the optimization was to change i++ to ++i in for loop statements.

之前优化

for (i=0;i<1;i++) {}

for (var i = 0, j = 0; i < 1000000; i++, j++) {
    if (i == 4) {
        var tmp = i / 2;
    }

    if ((i % 2) == 0) {
        var tmp = i / 2;
        i++;
    }
}
var arr = new Array(1000000);
for (i = 0; i < arr.length; i++) {}

优化后

for(var i=0;i<1;++i){}
for(var i=0,j=0;i<1000000;++i,++j){if(i==4){var tmp=i>>1;}
if((i&1)==0){var tmp=i>>1;i++;}}
var arr=new Array(1000000);for(var i=0,arr_len=arr.length;i<arr_len;++i){}

我知道前后增量的作用，但是任何想法如何加速代码？

I know what pre and post increments do, but any idea how does this speeds the code up?

推荐答案

这是我读到的，可以回答你的问题：preincrement（ ++ i ）在 i 的值中加1，然后返回 i ;相反， i ++ 返回 i 然后加一个，理论上 导致在应用增量操作之前创建存储 i 值的临时变量。

This is what I read and could answer your question: "preincrement (++i) adds one to the value of i, then returns i; in contrast, i++ returns i then adds one to it, which in theory results in the creation of a temporary variable storing the value of i before the increment operation was applied".

这篇关于后增量与预增量 - Javascript优化的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！