JavaScript正则表达式是一种用于模式匹配和文本操作的强大工具。它允许你使用简洁的语法来查找、替换或验证字符串中的特定子串。以下是一些基本的正则表达式定义及其示例:,,### 基本正则表达式,,1. **简单匹配**:, ``javascript, let str = "Hello, World!";, let pattern = /World/;, console.log(pattern.test(str)); // 输出: true,
`,,2. **捕获组**:,
`javascript, let str = "Hello, World!";, let pattern = /(Hello)/;, let match = pattern.exec(str);, console.log(match[1]); // 输出: Hello,
`,,3. **分组**:,
`javascript, let str = "Hello, World!";, let pattern = /(\w+)/g; // g 表示全局搜索, let matches = str.match(pattern);, console.log(matches); // 输出: ["Hello", "World!"],
`,,4. **负向前瞻和负向后瞻**:,
`javascript, let str = "The quick brown fox jumps over the lazy dog.";, let pattern = /\b(?!fox\b)\w+\b/g;, let matches = str.match(pattern);, console.log(matches); // 输出: ["The", "quick", "brown", "jumps", "over", "the", "lazy", "dog."],
`,,5. **字符类**:,
`javascript, let str = "Hello, World!";, let pattern = /[a-zA-Z]/g;, let matches = str.match(pattern);, console.log(matches); // 输出: ["H", "e", "l", "l", "o", ",", " ", "W", "o", "r", "l", "d", "!"],
`,,6. **特殊字符转义**:,
`javascript, let str = "Hello, World!";, let pattern = /,/g;, let matches = str.match(pattern);, console.log(matches); // 输出: [","],
`,,7. **反斜杠转义**:,
`javascript, let str = "Hello\\, World!";, let pattern = /\\/g;, let matches = str.match(pattern);, console.log(matches); // 输出: ["\\"],
`,,8. **Unicode字符**:,
`javascript, let str = "Hello, 世界!";, let pattern = /[^\u0000-\uFFFF]/g;, let matches = str.match(pattern);, console.log(matches); // 输出: ["Hello,", " ", "世界!"],
`,,9. **边界匹配**:,
`javascript, let str = "Hello, World!";, let pattern = /^\w+$/;, let result = pattern.test(str);, console.log(result); // 输出: false,
``,,这些是正则表达式的基础用法。通过组合各种特性,你可以实现更复杂的模式匹配需求。
js正则表达式怎么定义?
javascript正则表达式的2种定义方法:一种是直接调用RegExp(),第二种是直接用字面量来定义,即var re = /正则规则/。
js正则表达式的2种定义方法本质都是调用RegExp()方法在调用同一段正则代码的时候,ECMAScript3和ECMAScript5中表现完全不一样function reg(){ var re = /\sjavascript/; return re; }分别在ECMAScript3和ECMAScript5中调用reg()方法多次在ECMAScript3中,调用的是同一个RegExp对象,在ECMAScript5中,调用的是不同的RegExp对象 因为在EXCMAScript5中每执行一次,就生成一个新的RegExp对象所以在ECMAScript3中会造成程序的隐患,因为只要在一个地方对这个对象进行修改的话,所有调用到这个对象的地方都会变化。
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