## 概述

length 属性表示一个字符串的长度。

## 描述

该属性返回字符串中字符编码单元的数量。JavaScript 使用 UTF-16 编码，该编码使用一个 16 比特的编码单元来表示大部分常见的字符，使用两个代码单元表示不常用的字符。因此 length 返回值可能与字符串中实际的字符数量不相同。

空字符串的 `length` 为 0。

静态属性 String.length 返回 1。

## 示例

    var x = "Mozilla";
    var empty = "";

    console.log("Mozilla is " + x.length + " code units long");
    /* "Mozilla is 7 code units long" */

    console.log("The empty string is has a length of " + empty.length);
    /* "The empty string is has a length of 0" */

## 规范

Specification | Status | Comment
--- | --- | ---
ECMAScript 1st Edition (ECMA-262) | Standard | Initial definition. Implemented in JavaScript 1.0.
ECMAScript 5.1 (ECMA-262) String.prototype.length | Standard |
ECMAScript 2015 (6th Edition, ECMA-262) String.prototype.length | Standard |

## 浏览器兼容性

We're converting our compatibility data into a machine-readable JSON format. This compatibility table still uses the old format, because we haven't yet converted the data it contains. Find out how you can help!

- Desktop
- Mobile

Feature | Chrome | Firefox (Gecko) | Internet Explorer | Opera | Safari
--- | --- | --- | --- | --- | ---
Basic support | (Yes) | (Yes) | (Yes) | (Yes) | (Yes)

Feature | Android | Chrome for Android | Firefox Mobile (Gecko) | IE Mobile | Opera Mobile | Safari Mobile
--- | --- | --- | --- | --- | --- | ---
Basic support | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes)

## 相关链接

- JavaScript String.length and Internationalizing Web Applications