例如:
<code>[\w.]+和[\w.+*?] </code>
这些符号在[]里面与外面有什么区别?
回复内容:
例如:
<code>[\w.]+和[\w.+*?] </code>
这些符号在[]里面与外面有什么区别?
首先正则表达式[]
里面的内容代表可选组合的意思,
类似
<code>/[\w.]/.test("a"); // true /[\w.]/.test("."); // true /[\w.]/.test("a."); // true /[\w.]/.test(" "); // false</code>
上面的正则表达式可选组合中可以匹配一个字符,或者一个点号,但是不能匹配空字符;
说说区别:
1..
在[]
里面的时候,它就是为了匹配.
的,在外面的时候它用来匹配任意字符的,见下面这个示例:
<code>/./.test(" "); //true /[.]/.test(" "); //false</code>
2.*
和+
在[]
外面被称为量词(数量词的量词),是表示要匹配的数量的,*
表示任意数量,集合表示是[0, +00)
;+
表示至少1次,集合表示是[1, +00)
;
不得不说的是,作为量词时,*
和+
前面必须跟着匹配含义的正则表达式(部分);
在[]
内就表示它本身的意义了,为了匹配*
或者+
;
<code>/[+]/.test("+"); //true /+/.test(""); //Uncaught SyntaxError: Invalid regular expression: /+/: Nothing to repeat(…) /.+/.test("oops"); //true</code>

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