From 33058f2b292b3a581333bdfb21b8f671898c5060 Mon Sep 17 00:00:00 2001 From: Peter Bengtsson Date: Tue, 8 Dec 2020 14:40:17 -0500 Subject: initial commit --- .../global_objects/string/codepointat/index.html | 173 +++++++++++++++++++++ 1 file changed, 173 insertions(+) create mode 100644 files/zh-cn/web/javascript/reference/global_objects/string/codepointat/index.html (limited to 'files/zh-cn/web/javascript/reference/global_objects/string/codepointat/index.html') diff --git a/files/zh-cn/web/javascript/reference/global_objects/string/codepointat/index.html b/files/zh-cn/web/javascript/reference/global_objects/string/codepointat/index.html new file mode 100644 index 0000000000..567de8abc1 --- /dev/null +++ b/files/zh-cn/web/javascript/reference/global_objects/string/codepointat/index.html @@ -0,0 +1,173 @@ +--- +title: String.prototype.codePointAt() +slug: Web/JavaScript/Reference/Global_Objects/String/codePointAt +translation_of: Web/JavaScript/Reference/Global_Objects/String/codePointAt +--- +
{{JSRef}}
+ +

codePointAt() 方法返回 一个 Unicode 编码点值的非负整数。

+ +

语法

+ +
str.codePointAt(pos)
+ +

参数

+ +
+
pos
+
这个字符串中需要转码的元素的位置。
+
+ +

返回值

+ +

返回值是在字符串中的给定索引的编码单元体现的数字，如果在索引处没找到元素则返回 {{jsxref("undefined")}} 。

+ +

描述

+ +

如果在指定的位置没有元素则返回 {{jsxref("undefined")}} 。如果在索引处开始没有UTF-16 代理对，将直接返回在那个索引处的编码单元。

+ +

Surrogate Pair是UTF-16中用于扩展字符而使用的编码方式，是一种采用四个字节(两个UTF-16编码)来表示一个字符，称作代理对。

+ +

例子

+ +

使用 codePointAt()

+ +
'ABC'.codePointAt(1);          // 66
+'\uD800\uDC00'.codePointAt(0); // 65536
+
+'XYZ'.codePointAt(42); // undefined
+
+ +

替补支持(Polyfill)

+ +

给原生不支持 ECMAScript 6 的浏览器使用codePointAt()方法的的一个字符串扩展方法。

+ +
/*! http://mths.be/codepointat v0.1.0 by @mathias */
+if (!String.prototype.codePointAt) {
+  (function() {
+    'use strict'; // 严格模式，needed to support `apply`/`call` with `undefined`/`null`
+    var codePointAt = function(position) {
+      if (this == null) {
+        throw TypeError();
+      }
+      var string = String(this);
+      var size = string.length;
+      // 变成整数
+      var index = position ? Number(position) : 0;
+      if (index != index) { // better `isNaN`
+        index = 0;
+      }
+      // 边界
+      if (index < 0 || index >= size) {
+        return undefined;
+      }
+      // 第一个编码单元
+      var first = string.charCodeAt(index);
+      var second;
+      if ( // 检查是否开始 surrogate pair
+        first >= 0xD800 && first <= 0xDBFF && // high surrogate
+        size > index + 1 // 下一个编码单元
+      ) {
+        second = string.charCodeAt(index + 1);
+        if (second >= 0xDC00 && second <= 0xDFFF) { // low surrogate
+          // http://mathiasbynens.be/notes/javascript-encoding#surrogate-formulae
+          return (first - 0xD800) * 0x400 + second - 0xDC00 + 0x10000;
+        }
+      }
+      return first;
+    };
+    if (Object.defineProperty) {
+      Object.defineProperty(String.prototype, 'codePointAt', {
+        'value': codePointAt,
+        'configurable': true,
+        'writable': true
+      });
+    } else {
+      String.prototype.codePointAt = codePointAt;
+    }
+  }());
+}
+
+ +

规范

+ + + + + + + + + + + + + + + + + + + +
SpecificationStatusComment
{{SpecName('ES6', '#sec-string.prototype.codepointat', 'String.prototype.codePointAt')}}{{Spec2('ES6')}}Initial definition.
{{SpecName('ESDraft', '#sec-string.prototype.codepointat', 'String.prototype.codePointAt')}}{{Spec2('ESDraft')}} 
+ +

浏览器兼容性

+ +
{{CompatibilityTable}}
+ +
+ + + + + + + + + + + + + + + + + + + +
特性ChromeFirefox (Gecko)Internet ExplorerOperaSafari
基本支持{{CompatChrome("41")}}{{CompatGeckoDesktop("29")}}11{{CompatOpera("28")}}{{CompatNo}}
+
+ +
+ + + + + + + + + + + + + + + + + + + + + +
特性AndroidChrome for AndroidFirefox Mobile (Gecko)IE MobileOpera MobileSafari Mobile
基本支持{{CompatNo}}{{CompatNo}}{{CompatGeckoMobile("29")}}{{CompatNo}}{{CompatNo}}{{CompatNo}}
+
+ +

相关链接

+ + -- cgit v1.2.3-54-g00ecf