第九周作业

regular expression rules 正则表达式

正则表达式是用于匹配字符串中字符组合的模式。在 JavaScript中，正则表达式也是对象。这些模式被用于 RegExp 的 exec 和 test 方法, 以及 String 的 match、replace、search 和 split 方法。本章介绍 JavaScript正则表达式。

创建一个正则表达式

 1、使用一个正则表达式字面量，其由包含在斜杠之间的模式组成，如下所示：

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<code class=" language-js"><span class="token comment">/*    /pattern/flags */   <span class="token keyword">const regex <span class="token operator">= <span class="token regex">/ab+c/<span class="token punctuation">;   <span class="token keyword">const regex <span class="token operator">= <span class="token regex">/^[a-zA-Z]+[0-9]*W?_$/gi<span class="token punctuation">;</span></span></span></span></span></span></span></span></span></code>在加载脚本后，正则表达式字面值提供正则表达式的编译。当正则表达式保持不变时，使用此方法可获得更好的性能。<br><br>2、调用<code><a title="zh-CN/docs/JavaScript/Reference/Global Objects/RegExp" href="https://developer.mozilla.org/zh-CN/docs/JavaScript/Reference/Global_Objects/RegExp">RegExp</a></code>对象的构造函数

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<code class=" language-js"><span class="token comment">/*     new RegExp(pattern [, flags]) */   <span class="token keyword">let regex <span class="token operator">= <span class="token keyword">new <span class="token class-name">RegExp<span class="token punctuation">(<span class="token string">"ab+c"<span class="token punctuation">)<span class="token punctuation">;   <span class="token keyword">let regex <span class="token operator">= <span class="token keyword">new <span class="token class-name">RegExp<span class="token punctuation">(<span class="token regex">/^[a-zA-Z]+[0-9]*W?_$/<span class="token punctuation">, <span class="token string">"gi"<span class="token punctuation">)<span class="token punctuation">;   <span class="token keyword">let regex <span class="token operator">= <span class="token keyword">new <span class="token class-name">RegExp<span class="token punctuation">(<span class="token string">"^[a-zA-Z]+[0-9]*\W?_$"<span class="token punctuation">, <span class="token string">"gi"<span class="token punctuation">)<span class="token punctuation">;<br><br></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></code>