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 | 128 +++++++++++++++++++++ 1 file changed, 128 insertions(+) create mode 100644 files/ja/web/javascript/reference/global_objects/string/repeat/index.html (limited to 'files/ja/web/javascript/reference/global_objects/string/repeat') diff --git a/files/ja/web/javascript/reference/global_objects/string/repeat/index.html b/files/ja/web/javascript/reference/global_objects/string/repeat/index.html new file mode 100644 index 0000000000..4304fd9786 --- /dev/null +++ b/files/ja/web/javascript/reference/global_objects/string/repeat/index.html @@ -0,0 +1,128 @@ +--- +title: String.prototype.repeat() +slug: Web/JavaScript/Reference/Global_Objects/String/repeat +tags: + - ECMAScript 2015 + - JavaScript + - Method + - Prototype + - Reference + - String +translation_of: Web/JavaScript/Reference/Global_Objects/String/repeat +--- +
{{JSRef}}
+ +

repeat() メソッドは、呼び出し元の文字列を指定した数だけコピーして結合した新しい文字列を構築して返します。

+ +
{{EmbedInteractiveExample("pages/js/string-repeat.html","shorter")}}
+ + + +

構文

+ +
str.repeat(count)
+ +

引数

+ +
+
count
+
0 から{{jsxref("Global_Objects/Number/POSITIVE_INFINITY", "正の無限大")}}までの間の整数で、文字列を繰り返す数を示します。
+
+ +

返値

+ +

与えられた文字列の指定した回数分のコピーを含む新しい文字列です。

+ +

例外

+ + + +

例

+ +

repeat() の使用

+ +
'abc'.repeat(-1)    // RangeError
+'abc'.repeat(0)     // ''
+'abc'.repeat(1)     // 'abc'
+'abc'.repeat(2)     // 'abcabc'
+'abc'.repeat(3.5)   // 'abcabcabc' (小数は丸められ、整数の結果が返されます)
+'abc'.repeat(1/0)   // RangeError
+
+({ toString: () => 'abc', repeat: String.prototype.repeat }).repeat(2)
+// 'abcabc' (repeat() は汎用メソッドです)
+
+ +

ポリフィル

+ +

このメソッドは ECMAScript 2015 仕様で追加されたため、まだすべての JavaScript の実装で使用できるわけではありません。しかし、次のスニペットで String.prototype.repeat() を代替することができます。

+ +
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;
+    // To convert string to integer.
+    count = +count;
+    // Check NaN
+    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 '';
+
+    // Ensuring count is a 31-bit integer allows us to heavily optimize the
+    // main part. But anyway, most current (August 2014) browsers can't handle
+    // strings 1 << 28 chars or longer, so:
+    if (str.length * count >= 1 << 28)
+      throw new RangeError('repeat count must not overflow maximum string size');
+
+    var maxCount = str.length * count;
+    count = Math.floor(Math.log(count) / Math.log(2));
+    while (count) {
+       str += str;
+       count--;
+    }
+    str += str.substring(0, maxCount - str.length);
+    return str;
+  }
+}
+
+ +

仕様書

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

ブラウザーの互換性

+ + + +

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

+ +

関連情報

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