在JavaScript中复制数组的最快方法-切片与“ for”循环

本文翻译自：Fastest way to duplicate an array in JavaScript - slice vs. 'for' loop

In order to duplicate an array in JavaScript: which of the following is faster to use? 为了在JavaScript中复制数组，请使用以下哪项更快？

Slice method 切片方法

var dup_array = original_array.slice();

`For` loop `For`循环

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

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, and therefore both arrays will have references to the same objects. 我知道这两种方法都只能进行浅表复制：如果original_array包含对对象的引用，则不会克隆对象，但只会复制引用，因此两个数组都将引用相同的对象。 But this is not the point of this question. 但这不是这个问题的重点。

I'm asking only about speed. 我只问速度。

#1楼

参考：https://stackoom.com/question/GgzE/在JavaScript中复制数组的最快方法-切片与-for-循环

#2楼

There are at least 5 (!) ways to clone an array: 至少有5种（！）克隆数组的方法：

loop 环
slice 切片
Array.from() Array.from（）
concat 康卡特
spread operator (FASTEST) 点差算子（FASTEST）

There has been a huuuge BENCHMARKS thread , providing following information: 有一个很棒的BENCHMARKS线程，提供以下信息：

for blink browsers slice() is the fastest method, concat() is a bit slower, and while loop is 2.4x slower. 对于眨眼的浏览器， slice()是最快的方法， concat()慢一点， while loop慢2.4倍。
for other browsers while loop is the fastest method, since those browsers don't have internal optimizations for slice and concat . 对于其他浏览器， while loop是最快的方法，因为这些浏览器没有对slice和concat进行内部优化。

This remains true in Jul 2016. 2016年7月仍然如此。

Below are simple scripts that you can copy-paste into your browser's console and run several times to see the picture. 以下是一些简单的脚本，您可以将其复制粘贴到浏览器的控制台中，然后运行几次以查看图片。 They output milliseconds, lower is better. 他们输出毫秒，越低越好。

while loop while循环

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 切片

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

Please note that these methods will clone the Array object itself, array contents however are copied by reference and are not deep cloned. 请注意，这些方法将克隆Array对象本身，但是数组内容是通过引用复制的，因此不会进行深度克隆。

origAr == clonedArr //returns false
origAr[0] == clonedArr[0] //returns true

#3楼

Technically slice is the fastest way. 从技术上讲， slice 是最快的方法。 However , it is even faster if you add the 0 begin index. 但是，如果添加0开始索引，它甚至更快。

myArray.slice(0);

is faster than 比...快

myArray.slice();

http://jsperf.com/cloning-arrays/3 http://jsperf.com/cloning-arrays/3

#4楼

There is a much cleaner solution: 有一个更清洁的解决方案：

var srcArray = [1, 2, 3];
var clonedArray = srcArray.length === 1 ? [srcArray[0]] : Array.apply(this, srcArray);

The length check is required, because the Array constructor behaves differently when it is called with exactly one argument. 长度检查是必需的，因为当仅使用一个参数调用Array构造函数时，其行为会有所不同。

#5楼

深度克隆数组或对象的最简单方法：

var dup_array = JSON.parse(JSON.stringify(original_array))

#6楼

es6方式呢？

arr2 = [...arr1];