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/fromcodepoint/index.html | 144 +++++++++++++++++++++ 1 file changed, 144 insertions(+) create mode 100644 files/zh-cn/web/javascript/reference/global_objects/string/fromcodepoint/index.html (limited to 'files/zh-cn/web/javascript/reference/global_objects/string/fromcodepoint') diff --git a/files/zh-cn/web/javascript/reference/global_objects/string/fromcodepoint/index.html b/files/zh-cn/web/javascript/reference/global_objects/string/fromcodepoint/index.html new file mode 100644 index 0000000000..786125e340 --- /dev/null +++ b/files/zh-cn/web/javascript/reference/global_objects/string/fromcodepoint/index.html @@ -0,0 +1,144 @@ +--- +title: String.fromCodePoint() +slug: Web/JavaScript/Reference/Global_Objects/String/fromCodePoint +translation_of: Web/JavaScript/Reference/Global_Objects/String/fromCodePoint +--- +
{{JSRef}}
+ +

String.fromCodePoint() 静态方法返回使用指定的代码点序列创建的字符串。

+ +
{{EmbedInteractiveExample("pages/js/string-fromcodepoint.html")}}
+ + + +

语法

+ +
String.fromCodePoint(num1[, ...[, numN]])
+ +

参数

+ +
+
num1, ..., numN
+
一串 Unicode 编码位置，即“代码点”。
+
+

返回值

+ +

使用指定的 Unicode 编码位置创建的字符串。

+
+
+ +

异常

+ +
+
{{jsxref("RangeError")}}
+
如果传入无效的 Unicode 编码，将会抛出一个{{jsxref("RangeError")}} (例如： "RangeError: NaN is not a valid code point")。
+
+ +

说明

+ +

该方法返回一个字符串，而不是一个 {{jsxref("String")}} 对象。

+ +

因为 fromCodePoint() 是 {{jsxref("String")}} 的一个静态方法，所以只能通过 String.fromCodePoint() 这样的方式来使用，不能在你创建的 {{jsxref("String")}} 对象实例上直接调用。

+ +

例子

+ +

使用 fromCodePoint()

+ +
String.fromCodePoint(42);       // "*"
+String.fromCodePoint(65, 90);   // "AZ"
+String.fromCodePoint(0x404);    // "\u0404"
+String.fromCodePoint(0x2F804);  // "\uD87E\uDC04"
+String.fromCodePoint(194564);   // "\uD87E\uDC04"
+String.fromCodePoint(0x1D306, 0x61, 0x1D307) // "\uD834\uDF06a\uD834\uDF07"
+
+String.fromCodePoint('_');      // RangeError
+String.fromCodePoint(Infinity); // RangeError
+String.fromCodePoint(-1);       // RangeError
+String.fromCodePoint(3.14);     // RangeError
+String.fromCodePoint(3e-2);     // RangeError
+String.fromCodePoint(NaN);      // RangeError
+
+ +
// String.fromCharCode() 方法不能单独获取在高代码点位上的字符
+// 另一方面，下列的示例中，可以返回 4 字节，也可以返回 2 字节的字符
+// (也就是说，它可以返回单独的字符，使用长度 2 代替 1!）
+console.log(String.fromCodePoint(0x2F804)); // or 194564 in decimal
+
+ +

Polyfill

+ +

String.fromCodePoint 方法是 ECMAScript2015（ES6）新增加的特性，所以一些老的浏览器可能还不支持。可以通过使用下面的 polyfill 代码来保证浏览器的支持：

+ +
if (!String.fromCodePoint) (function(stringFromCharCode) {
+    var fromCodePoint = function(_) {
+      var codeUnits = [], codeLen = 0, result = "";
+      for (var index=0, len = arguments.length; index !== len; ++index) {
+        var codePoint = +arguments[index];
+        // correctly handles all cases including `NaN`, `-Infinity`, `+Infinity`
+        // The surrounding `!(...)` is required to correctly handle `NaN` cases
+        // The (codePoint>>>0) === codePoint clause handles decimals and negatives
+        if (!(codePoint < 0x10FFFF && (codePoint>>>0) === codePoint))
+          throw RangeError("Invalid code point: " + codePoint);
+        if (codePoint <= 0xFFFF) { // BMP code point
+          codeLen = codeUnits.push(codePoint);
+        } else { // Astral code point; split in surrogate halves
+          // https://mathiasbynens.be/notes/javascript-encoding#surrogate-formulae
+          codePoint -= 0x10000;
+          codeLen = codeUnits.push(
+            (codePoint >> 10) + 0xD800,  // highSurrogate
+            (codePoint % 0x400) + 0xDC00 // lowSurrogate
+          );
+        }
+        if (codeLen >= 0x3fff) {
+          result += stringFromCharCode.apply(null, codeUnits);
+          codeUnits.length = 0;
+        }
+      }
+      return result + stringFromCharCode.apply(null, codeUnits);
+    };
+    try { // IE 8 only supports `Object.defineProperty` on DOM elements
+      Object.defineProperty(String, "fromCodePoint", {
+        "value": fromCodePoint, "configurable": true, "writable": true
+      });
+    } catch(e) {
+      String.fromCodePoint = fromCodePoint;
+    }
+}(String.fromCharCode));
+
+ +

规范

+ + + + + + + + + + + + + + + + + + + +
规范状态备注
{{SpecName('ES2015', '#sec-string.fromcodepoint', 'String.fromCodePoint')}}{{Spec2('ES2015')}}Initial definition.
{{SpecName('ESDraft', '#sec-string.fromcodepoint', 'String.fromCodePoint')}}{{Spec2('ESDraft')}} 
+ +

浏览器兼容性

+ + + +

{{Compat("javascript.builtins.String.fromCodePoint")}}

+ +

参见

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