通过使用点添加值将数组更改为Object（大写） [英] changing an array to an Object (upper case) by adding a value using a dot

问题描述

使用点表示法向数组添加属性是否将其更改为对象？

Does adding a property to an array with dot notation change it to an object?

var arr = [];

arr.something = "test";

它是一个数组吗？

I不这么认为，但是underscore.js说它是

I don't think so, but underscore.js says it is

console.log( _.isArray(arr) );  //true

http ：//jsfiddle.net/wZcyG/

推荐答案

如果你看一下underscore.js 来源，您会看到 isArray 函数被定义为：

If you look at the underscore.js source, you will see that the isArray function is defined as:

 _.isArray = nativeIsArray || function(obj) {
    return toString.call(obj) == '[object Array]';
  };

浏览器的原生 Array.isArray 表示它是一个数组，因为它是被实例化的。如果浏览器没有本机 isArray ，则underscore.js使用第二个选项：比较 toString 对象，看它是否匹配字符串 [object Array] 。

The brower's native Array.isArray says it's an array because that's what it has been instantiated as. If the browser doesn't have a native isArray, then underscore.js uses the second option: comparing toString on the object to see if it matches the string [object Array].

简单地添加属性不足以改变对象的类型（根据JavaScript虚拟机，它仍然是恰好是数组的对象）。 JavaScript是一种动态语言，这意味着您可以向内置对象添加属性，但这样做并不会改变它们的内容;你只是扩展了他们。例如，Prototype.js用于通过向它们添加额外属性来扩展本机对象（如迭代器，过滤器，映射函数等）。

Simply adding a property is not enough to change the type of the object (according to the JavaScript virtual machine, it is still an object that happens to be an array). JavaScript is a dynamic language which means that you can add properties to in-built objects, but doing so does not change what they are; you have merely extended them. For example, Prototype.js used to extend native objects by adding extra properties to them (like iterators, filters, mapping functions, etc.).

您可以看到行为在Chrome中非常容易：

You can see the behavior in Chrome pretty easily:

> var arr = [];
  arr.something = "test";

> Array.isArray(arr);
  true

> toString.call(arr);
  "[object Array]"

编辑

数组不会丢失长度属性：

> var arr = [1, 2, 3];
  arr.something = "test";
  console.log(arr.length, arr.something);

  3 "test"

请注意，浏览器报告了正确的长度 3 以及测试的某些属性的正确值。

Notice that the browser reported the correct length of 3 and the correct value for test for the something property.

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