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/repeat/index.html | 124 +++++++++++++++++++++ 1 file changed, 124 insertions(+) create mode 100644 files/zh-cn/web/javascript/reference/global_objects/string/repeat/index.html (limited to 'files/zh-cn/web/javascript/reference/global_objects/string/repeat') diff --git a/files/zh-cn/web/javascript/reference/global_objects/string/repeat/index.html b/files/zh-cn/web/javascript/reference/global_objects/string/repeat/index.html new file mode 100644 index 0000000000..ce35065f1a --- /dev/null +++ b/files/zh-cn/web/javascript/reference/global_objects/string/repeat/index.html @@ -0,0 +1,124 @@ +--- +title: String.prototype.repeat() +slug: Web/JavaScript/Reference/Global_Objects/String/repeat +tags: + - ECMAScript 2015 + - ES 6 + - JavaScript + - Method + - Prototype + - Reference + - String + - polyfill + - repeat() + - 填充 +translation_of: Web/JavaScript/Reference/Global_Objects/String/repeat +--- +

{{JSRef}}

+ +

repeat() 构造并返回一个新字符串，该字符串包含被连接在一起的指定数量的字符串的副本。

+ +

语法

+ +
str.repeat(count)
+ +

参数

+ +
+
count
+
介于 0 和 {{jsxref("Global_Objects/Number/POSITIVE_INFINITY", "+Infinity")}} 之间的整数。表示在新构造的字符串中重复了多少遍原字符串。
+
+ +

返回值

+ +

 包含指定字符串的指定数量副本的新字符串。

+ +

Exceptions

+ + + +

兼容补丁(Polyfill)

+ +

此方法已添加到 ECMAScript 2015 规范中，并且可能尚未在所有 JavaScript 实现中可用。然而，你可以使用以下代码段对 String.prototype.repeat() 进行填充：

+ +
if (!String.prototype.repeat) {
+  String.prototype.repeat = function(count) {
+    'use strict';
+    if (this == null) {
+      throw new TypeError('can\'t convert ' + this + ' to object');
+    }
+    var str = '' + this;
+    count = +count;
+    if (count != count) {
+      count = 0;
+    }
+    if (count < 0) {
+      throw new RangeError('repeat count must be non-negative');
+    }
+    if (count == Infinity) {
+      throw new RangeError('repeat count must be less than infinity');
+    }
+    count = Math.floor(count);
+    if (str.length == 0 || count == 0) {
+      return '';
+    }
+    // 确保 count 是一个 31 位的整数。这样我们就可以使用如下优化的算法。
+    // 当前（2014年8月），绝大多数浏览器都不能支持 1 << 28 长的字符串，所以：
+    if (str.length * count >= 1 << 28) {
+      throw new RangeError('repeat count must not overflow maximum string size');
+    }
+    var rpt = '';
+    for (;;) {
+      if ((count & 1) == 1) {
+        rpt += str;
+      }
+      count >>>= 1;
+      if (count == 0) {
+        break;
+      }
+      str += str;
+    }
+    return rpt;
+  }
+}
+ + +

示例

+ +
"abc".repeat(-1)     // RangeError: repeat count must be positive and less than inifinity
+"abc".repeat(0)      // ""
+"abc".repeat(1)      // "abc"
+"abc".repeat(2)      // "abcabc"
+"abc".repeat(3.5)    // "abcabcabc" 参数count将会被自动转换成整数.
+"abc".repeat(1/0)    // RangeError: repeat count must be positive and less than inifinity
+
+({toString : () => "abc", repeat : String.prototype.repeat}).repeat(2)
+//"abcabc",repeat是一个通用方法,也就是它的调用者可以不是一个字符串对象.
+ +

规范

+ + + + + + + + + + + + +
规范
{{SpecName('ESDraft', '#sec-string.prototype.repeat', 'String.prototype.repeat')}}
+ +

浏览器兼容性

+ +

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

+ +

相关链接

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