在javascript中定义数组 [英] defining array in javascript

问题描述

我想在 javascript 中创建一个数组并记住两种方法，所以我只想知道根本区别是什么，以及这两种样式"是否存在性能差异

I want to create an array in javascript and remember two ways of doing it so I just want to know what the fundamental differences are and if there is a performance difference in these two "styles"

var array_1 = new Array("fee","fie","foo","fum");
var array_2 = ['a','b','c'];

for (let i=0; i<array_1.length; i++){
  console.log(array_1[i])
}

for (let i=0; i<array_2.length; i++){
  console.log(array_2[i])
}

推荐答案

他们做同样的事情.[] 符号的优点是:

They do the same thing. Advantages to the [] notation are:

• 它更短.
• 如果有人做了一些愚蠢的事情，比如重新定义 Array 符号，它仍然有效.
• 当您只定义一个条目时没有歧义，而当您编写 new Array(3) 时，如果您习惯于看到在构造函数中列出的条目，您很容易将其误读为意味着 [3]，实际上它创建了一个 length 为 3 且没有条目的新数组.
• 它可能会更快一点点(取决于 JavaScript 实现)，因为当你说 new Array 时，解释器必须去查找 Array 符号，这意味着遍历作用域链中的所有条目，直到它到达全局对象并找到它，而使用 [] 则不需要这样做.在正常用例中产生任何实际现实世界影响的可能性很低.尽管如此……

• It's shorter.
• If someone does something silly like redefine the Array symbol, it still works.
• There's no ambiguity when you only define a single entry, whereas when you write new Array(3), if you're used to seeing entries listed in the constructor, you could easily misread that to mean [3], when in fact it creates a new array with a length of 3 and no entries.
• It may be a tiny little bit faster (depending on JavaScript implementation), because when you say new Array, the interpreter has to go look up the Array symbol, which means traversing all entries in the scope chain until it gets to the global object and finds it, whereas with [] it doesn't need to do that. The odds of that having any tangible real-world impact in normal use cases are low. Still, though...

所以使用[]有几个很好的理由.

So there are several good reasons to use [].

新数组的优势:

• 可以设置数组的初始长度，例如，var a = new Array(3);

几年来我没有任何理由这样做(自从得知 数组并不是真正的数组，并且尝试预先分配它们是没有意义的).如果你真的想要，你可以随时这样做:

I haven't had any reason to do that in several years (not since learning that arrays aren't really arrays and there's no point trying to pre-allocate them). And if you really want to, you can always do this:

var a = [];
a.length = 3;

这篇关于在javascript中定义数组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！