JavaScript对象的长度 [英] Length of a JavaScript object

问题描述

如果我有一个JavaScript对象，请说

If I have a JavaScript object, say

var myObject = new Object();
myObject["firstname"] = "Gareth";
myObject["lastname"] = "Simpson";
myObject["age"] = 21;

是否有内置或接受的最佳实践方法来获取此对象的长度？

is there a built-in or accepted best practice way to get the length of this object?

推荐答案

最强大的答案（即捕获您尝试做的事情的意图，同时导致最少的错误）将是：

The most robust answer (i.e. that captures the intent of what you're trying to do while causing the fewest bugs) would be:

Object.size = function(obj) {
    var size = 0, key;
    for (key in obj) {
        if (obj.hasOwnProperty(key)) size++;
    }
    return size;
};

// Get the size of an object
var size = Object.size(myArray);

JavaScript中有一种约定不要向Object.prototype添加内容，因为它可能会破坏各种库中的枚举。但是，向Object添加方法通常是安全的。

There's a sort of convention in JavaScript that you don't add things to Object.prototype, because it can break enumerations in various libraries. Adding methods to Object is usually safe, though.

这是2016年的更新， ES5的广泛部署及更高版本。对于IE9 +和所有其他支持ES5 +的现代浏览器，你可以使用 Object.keys（），所以上面的代码变为：

Here's an update as of 2016 and widespread deployment of ES5 and beyond. For IE9+ and all other modern ES5+ capable browsers, you can use Object.keys() so the above code just becomes:

var size = Object.keys(myObj).length;

这不需要修改任何现有的原型，因为 Object.keys（ ）现已内置。

This doesn't have to modify any existing prototype since Object.keys() is now built in.

编辑：对象可以具有无法通过Object返回的符号属性。关键方法。因此，如果不提及它们，答案将是不完整的。

Edit: Objects can have symbolic properties which can not be returned via Object.key method. So the answer would be incomplete without mentioning them.

符号类型已添加到语言中，以便为对象属性创建唯一标识符。 Symbol类型的主要好处是防止覆盖。

Symbol type was added to the language to create unique identifiers for object properties. Main benefit of Symbol type is prevention of overwrites.

Object.keys 或 Object。 getOwnPropertyNames 不适用于符号属性。要返回它们，您需要使用 Object.getOwnPropertySymbols 。

Object.keys or Object.getOwnPropertyNames does not work for symbolic properties. To return them you need to use Object.getOwnPropertySymbols.

var person = {
  [Symbol('name')]: 'John Doe',
  [Symbol('age')]: 33,
  "occupation": "Programmer"
};

const propOwn = Object.getOwnPropertyNames(person);
console.log(propOwn.length); // 1

let propSymb = Object.getOwnPropertySymbols(person);
console.log(propSymb.length); // 2

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