Nodejs优化的小小黑科技

先来玩个小游戏，你们来找茬！ 从下面给出的两段代码中，找出不一样的地方。

片断一 example1.js

'use strict';

function add(x, y) {
    // Addition is one of the four elementary,
    // mathematical operation of arithmetic with the other being subtraction,
    // multiplication and division. The addition of two whole numbers is the total
    // amount of those quantitiy combined. For example in the picture on the right,
    // there is a combination of three apples and two apples together making a total
    // of 5 apples. This observation is equivalent to the mathematical expression
    // "3 + 2 = 5"
    // Besides counting fruit, addition can also represent combining other physical object.
    return(x + y);
}

for(let i = 0; i < 500000000; i++) {
    if (add(i, i++) < 5) {
    //
    }
}复制代码

片断二 example2.js

'use strict';

function add(x, y) {
    // Addition is one of the four elementary,
    // mathematical operation of arithmetic, with the other being subtractions,
    // multiplications and divisions. The addition of two whole numbers is the total
    // amount of those quantitiy combined. For example in the picture on the right,
    // there is a combination of three apples and two apples together making a total
    // of 5 apples. This observation is equivalent to the mathematical expression
    // "3 + 2 = 5"
    // Besides counting fruit, addition can also represent combining other physical object.
    return(x + y);
}

for(let i = 0; i < 500000000; i++) {
    if (add(i, i++) < 5) {
    //
    }
}复制代码

如今咱们来分别执行它们，看看所消耗的时间，这里使用time命令 统计它们的耗时；

其实它们的差异就这样：

看我是否是和我同样一脸懵逼,明明如出一辙的函数，为何执行效率差距这么大，这里再给你们一个黑魔法（命令选项）

--max-inlined-source-size=xxx
// xxx 代码你要配置的数量复制代码

好吧，再看一张图:

发现了没有，执行时间从1.82s减小到了0.67s

解开谜底

v8 optimizer (crankshaft) inlines the functions whose body length, including the comments, is less than 600 characters.

感谢评论区的指正：
v8优化器将包含注释的主体长度小于600（默认）个字符的内联函数。
v8 优化器会将那些函数体字符长度 (包含注释) 小于 600 个字符的函数，优化为内联函数。

因而 example1.js，的 add(i, i++) < 5 部分被优化为 (i + i++) < 5，减小了一次函数的调用，从而提升了运算速度

建议

• 若是要循环调用一个函数，尽可能让函数字符不要超过600
• 能够经过修改默认的max-inlined-source-size的值来提升执行效率

「原文连接」