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• 描述
• 范例
• 规范
• 浏览器兼容性
• 另请参阅
• 相关话题

The legacy RegExp $1, $2, $3, $4, $5, $6, $7, $8, $9 properties are static and read-only properties of regular expressions that contain parenthesized substring matches.

描述

The $1, ..., $9 properties are static, they are not a property of an individual regular expression object. Instead, you always use them as RegExp.$1 , ..., RegExp.$9 .

The values of these properties are read-only and modified whenever successful matches are made.

The number of possible parenthesized substrings is unlimited, but the RegExp object can only hold the first nine. You can access all parenthesized substrings through the returned array's indexes.

These properties can be used in the replacement text for the String.replace method. When used this way, do not prepend them with RegExp . The example below illustrates this. When parentheses are not included in the regular expression, the script interprets $n 's literally (where n is a positive integer).

范例

Using $n with String.replace

The following script uses the replace() 方法在 String instance to match a name in the format first last and output it in the format last, first . In the replacement text, the script uses $1 and $2 to indicate the results of the corresponding matching parentheses in the regular expression pattern.

var re = /(\w+)\s(\w+)/;
var str = 'John Smith';
str.replace(re, '$2, $1'); // "Smith, John"
RegExp.$1; // "John"
RegExp.$2; // "Smith"
					

Using $n with RegExp.test

The following script uses the test() 方法在 RegExp instance to grab a number in a generic string.

var str = 'Test 24';
var number = /(\d+)/.test(str) ? RegExp.$1 : '0';
number; // "24"
					

Please note that any operation involving the usage of other regular expressions between a re.test(str) call and the RegExp.$n property, might have side effects, so that accessing these special properties should be done instantly, otherwise the result might be unexpected.

规范

规范
Legacy RegExp features in JavaScript

浏览器兼容性

The compatibility table on this page is generated from structured data. If you'd like to contribute to the data, please check out https://github.com/mdn/browser-compat-data and send us a pull request. 更新 GitHub 上的兼容性数据

	Desktop						Mobile						Server
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet	Node.js
RegExp.$1-$9	Chrome 1	Edge 12	Firefox 1	IE 4	Opera 5	Safari 1	WebView Android 1	Chrome Android 18	Firefox Android 4	Opera Android 10.1	Safari iOS 1	Samsung Internet Android 1.0	nodejs Yes

图例

完整支持

完整支持

另请参阅

• RegExp.input ($_)
• RegExp.lastMatch ($&)
• RegExp.lastParen ($+)
• RegExp.leftContext ($`)
• RegExp.rightContext ($')

元数据

• 最后修改： Aug 23, 2020

相关话题

1. 标准内置对象
2. RegExp
3. 特性
   1. RegExp.$1-$9
   2. RegExp.input ($_)
   3. RegExp.lastMatch ($&)
   4. RegExp.lastParen ($+)
   5. RegExp.leftContext ($`)
   6. RegExp.prototype.dotAll
   7. RegExp.prototype.flags
   8. RegExp.prototype.global
   9. RegExp.prototype.ignoreCase
   10. RegExp.prototype.multiline
   11. RegExp.prototype.source
   12. RegExp.prototype.sticky
   13. RegExp.prototype.unicode
   14. RegExp.rightContext ($')
   15. RegExpInstance.lastIndex
   16. get RegExp[@@species]
4. 方法
   1. RegExp.prototype.compile()
   2. RegExp.prototype.exec()
   3. RegExp.prototype.test()
   4. RegExp.prototype.toSource()
   5. RegExp.prototype.toString()
   6. RegExp.prototype[@@matchAll]()
   7. RegExp.prototype[@@match]()
   8. RegExp.prototype[@@replace]()
   9. RegExp.prototype[@@search]()
   10. RegExp.prototype[@@split]()
5. 继承：
6. Function
7. 特性
   1. Function.arguments
   2. Function.caller
   3. Function.displayName
   4. Function.length
   5. Function.name
8. 方法
   1. Function.prototype.apply()
   2. Function.prototype.bind()
   3. Function.prototype.call()
   4. Function.prototype.toSource()
   5. Function.prototype.toString()
9. Object
10. 特性
    1. Object.prototype.__proto__
    2. Object.prototype.constructor
11. 方法
    1. Object.prototype.__defineGetter__()
    2. Object.prototype.__defineSetter__()
    3. Object.prototype.__lookupGetter__()
    4. Object.prototype.__lookupSetter__()
    5. Object.prototype.hasOwnProperty()
    6. Object.prototype.isPrototypeOf()
    7. Object.prototype.propertyIsEnumerable()
    8. Object.prototype.toLocaleString()
    9. Object.prototype.toSource()
    10. Object.prototype.toString()
    11. Object.prototype.valueOf()
    12. Object.setPrototypeOf()