Javascript最快的方式来复制一个Array - slice vs for loop [英] Javascript fastest way to duplicate an Array - slice vs for loop

问题描述

为了在Javascript中复制数组，

任何人都知道（也许测试）如果使用更快：

切片方法：

  var dup_array = original_array.slice 
  

或 For循环：

  for（var i = 0，len = original_array.length; i  dup_array [i] = original_array [i] 
  

---

更新:(为了澄清自己）两个方法只做一个浅拷贝：如果original_array包含对对象的引用，对象不会被克隆，但只有引用将被复制，因此两个数组都将引用相同的对象。
但这不是这个问题的要点。

我只是问速度。

解决方案

克隆数组至少有 5 （！）种方法：

• 循环


• 切片


• Array.from（）


• 
  
• 传播运算符等（很慢，现在忘记了）

提供了以下信息： BENCHMARKS主题，提供以下信息：

code 有点慢， while循环慢2.4倍。



• 其他浏览器 while 是最快的方法，因为这些浏览器没有内部优化切片和 concat 。

这在2016年7月仍然如此。

以下是简单的脚本，您可以复制 - 粘贴到浏览器的控制台，图片。

 
  n = 1000 * 1000; 
 start = + new Date（）; 
 a = Array（n）; 
 b = Array（n）; 
 i = a.length; 
 while（i--）b [i] = a [i]; 
 console.log（new Date（） -  start）; 
  

切片

  n = 1000 * 1000; 
 start = + new Date（）; 
 a = Array（n）; 
 b = a.slice（）; 
 console.log（new Date（） -  start）; 
  

In order to duplicate an Array in Javascript,

does anyone know (and maybe tested) if it's faster to use:

Slice method:

var dup_array = original_array.slice();

or For loop:

for(var i = 0, len = original_array.length; i < len; ++i)
   dup_array[i] = original_array[i];

---

UPDATE: (just to clarify myself) I know both ways do only a shallow copy: if original_array contains references to objects, objects won't be cloned, but only the references will be copied therefore both arrays will have references to the same objects. But this is not the point of this question.

I'm asking only about speed.

解决方案

There are at least 5 (!) ways to clone an array:

• loop
• slice
• Array.from()
• concat
• spread operator, etc. (so slow, forget it for now)

There has been a huuuge BENCHMARKS thread, providing following information:

• for blink browsers slice() is the fastest method, concat() is a bit slower, and while loop is 2.4x slower.

• for other browsers while loop is the fastest method, since those browsers don't have internal optimizations for slice and concat.

This remains true in Jul 2016.

Below are simple scripts that you can copy-paste into your browser's console and run several times to see the picture. They output milliseconds, lower is better.

while loop

n = 1000*1000;
start = + new Date();
a = Array(n); 
b = Array(n); 
i = a.length;
while(i--) b[i] = a[i];
console.log(new Date() - start);

slice

n = 1000*1000;
start = + new Date();
a = Array(n); 
b = a.slice();
console.log(new Date() - start);

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