如何在Javascript数组的开头添加新的数组元素？

本文翻译自：How can I add new array elements at the beginning of an array in Javascript?

I have a need to add or prepend elements at the beginning of an array. 我需要在数组的开头添加或添加元素。

For example, if my array looks like below: 例如，如果我的数组如下所示：

[23, 45, 12, 67]

And the response from my AJAX call is 34 , I want the updated array to be like the following: 我的AJAX调用的响应为34 ，我希望更新后的数组如下所示：

[34, 23, 45, 12, 67]

Currently I am planning to do it like this: 目前，我正在计划这样做：

var newArray = [];
newArray.push(response);

for (var i = 0; i < theArray.length; i++) {
    newArray.push(theArray[i]);
}

theArray = newArray;
delete newArray;

Is there any better way to do this? 有什么更好的方法吗？ Does Javascript have any built-in functionality that does this? Javascript是否具有执行此操作的任何内置功能？

The complexity of my method is O(n) and it would be really interesting to see better implementations. 我的方法的复杂度为O(n) ，看到更好的实现将真的很有趣。

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#1楼

参考：https://stackoom.com/question/XsKX/如何在Javascript数组的开头添加新的数组元素

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#2楼

Quick Cheatsheet: 快速备忘单：

The terms shift/unshift and push/pop can be a bit confusing, at least to folks who may not be familiar with programming in C. 术语“移位/不移位”和“推入/弹出”可能会有些混乱，至少对于那些可能不熟悉C编程的人而言。

If you are not familiar with the lingo, here is a quick translation of alternate terms, which may be easier to remember: 如果您对术语不熟悉，可以使用以下快速翻译的替代术语，这样可能更容易记住：

* array_unshift()  -  (aka Prepend ;; InsertBefore ;; InsertAtBegin )     
* array_shift()    -  (aka UnPrepend ;; RemoveBefore  ;; RemoveFromBegin )

* array_push()     -  (aka Append ;; InsertAfter   ;; InsertAtEnd )     
* array_pop()      -  (aka UnAppend ;; RemoveAfter   ;; RemoveFromEnd ) 

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#3楼

you have an array: var arr = [23, 45, 12, 67]; 您有一个数组： var arr = [23, 45, 12, 67];

To add an item to the beginning, you want to use splice : 要将项目添加到开头，您想使用splice ：

 var arr = [23, 45, 12, 67]; arr.splice(0, 0, 34) console.log(arr); 

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#4楼

Another way to do that through concat 通过concat做到这一点的另一种方法

 var arr = [1, 2, 3, 4, 5, 6, 7]; console.log([0].concat(arr)); 

The difference between concat and unshift is that concat returns a new array. 之间的差concat和unshift是concat返回一个新的数组。 The performance between them could be found here . 他们之间的表现可以在这里找到。

function fn_unshift() {
  arr.unshift(0);
  return arr;
}

function fn_concat_init() {
  return [0].concat(arr)
}

Here is the test result 这是测试结果

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#5楼

With ES6 , use the spread operator ... : 对于ES6，请使用传播运算符... ：

DEMO 演示

 var arr = [23, 45, 12, 67]; arr = [34, ...arr]; // RESULT : [34,23, 45, 12, 67] console.log(arr) 

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#6楼

 var testdata = new Array(); testdata = [23, 45, 12, 67]; testdata = [34, ...testdata]; console.log(testdata)