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[js][正则]你不知道的正则表达式之断言.html
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[js][正则]你不知道的正则表达式之断言.html
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<span data-v-7c5ab02c>2017 - </span>
2023
</a></span></div></div> <div data-v-5f3f4765><main class="page"><div class="page-title" style="display:none;"><h1>你不知道的正则表达式之断言</h1> <hr> <div data-v-2c863f0e><i class="iconfont reco-account" data-v-2c863f0e><span data-v-2c863f0e>JyLie</span></i> <i class="iconfont reco-date" data-v-2c863f0e><span data-v-2c863f0e>2022-02-23</span></i> <!----> <i class="iconfont reco-tag tags" data-v-2c863f0e><span class="tag-item" data-v-2c863f0e>RegExp</span></i></div></div> <div class="theme-reco-content content__default" style="display:none;"><h2 id="前言"><a href="#前言" class="header-anchor">#</a> 前言</h2> <p>今天在瞎搞 vue3 重构时用到了<code>require.content</code>，在使用<code>require.content</code>的时候用到了正则匹配文件路径的情景，于是重新回顾了一遍 JavaScript 正则匹配相关的内容。本次文章主要针对正则匹配的断言展开，面向在特殊情景下需要排除某个特定长度字段进行匹配。</p> <h2 id="基本概念"><a href="#基本概念" class="header-anchor">#</a> 基本概念</h2> <p>正则的断言离不开两个主要概念：</p> <ul><li>前瞻</li> <li>后瞻</li></ul> <p>前瞻 有分为 正向前瞻 和 负向前瞻。通俗讲为，以特定字符为基准<strong>往后</strong>匹配特定字符（串）。</p> <p>后瞻 有分为 正向后瞻 和 负向后瞻。通俗讲为，以特定字符为基准<strong>往前</strong>匹配特定字符（串）。</p> <p>前瞻、后瞻一览表，如下：</p> <table><thead><tr><th>表达式</th> <th>名称</th> <th>描述</th></tr></thead> <tbody><tr><td>(?=exp)</td> <td>正向前瞻</td> <td>匹配后面满足表达式 exp 的位置</td></tr> <tr><td>(?!exp)</td> <td>负向前瞻</td> <td>匹配后面不满足（排除）表达式 exp 的位置</td></tr> <tr><td>(?<=exp)</td> <td>正向后瞻</td> <td>匹配后面满足表达式 exp 的位置</td></tr> <tr><td>(?<!exp)</td> <td>负向后瞻</td> <td>匹配后面不满足（排除）表达式 exp 的位置</td></tr></tbody></table> <p>通过上述表格基本可以理解前瞻与后瞻的用途，主要用于匹配字符的位置。当然可以根据自身需求来判断是匹配满足（排除）某字符后面的字符（串），还是满足（排除）某字符前面的字符（串）。</p> <h2 id="情景交融"><a href="#情景交融" class="header-anchor">#</a> 情景交融</h2> <h3 id="基础案例"><a href="#基础案例" class="header-anchor">#</a> 基础案例</h3> <div class="language-js line-numbers-mode"><pre class="language-js"><code><span class="token comment">// 以Jy为基准往后看，是否紧跟着Lie字段</span>
<span class="token operator">/</span><span class="token function">Jy</span><span class="token punctuation">(</span><span class="token operator">?</span><span class="token operator">=</span>Lie<span class="token punctuation">)</span><span class="token operator">/</span>g<span class="token punctuation">.</span><span class="token function">test</span><span class="token punctuation">(</span><span class="token string">'JyLie'</span><span class="token punctuation">)</span>
<span class="token comment">// 以Jy为基准往后看，是否不紧跟着Lie字段</span>
<span class="token operator">/</span><span class="token function">Jy</span><span class="token punctuation">(</span><span class="token operator">?</span><span class="token operator">!</span>Lie<span class="token punctuation">)</span><span class="token operator">/</span>g<span class="token punctuation">.</span><span class="token function">test</span><span class="token punctuation">(</span><span class="token string">'JyLie'</span><span class="token punctuation">)</span>
<span class="token comment">// 以Jy为基准往前看，是否紧跟着Lie字段</span>
<span class="token operator">/</span><span class="token punctuation">(</span><span class="token operator">?</span><span class="token operator"><=</span>Lie<span class="token punctuation">)</span>Jy<span class="token operator">/</span>g<span class="token punctuation">.</span><span class="token function">test</span><span class="token punctuation">(</span><span class="token string">'LieJy'</span><span class="token punctuation">)</span>
<span class="token comment">// 以Jy为基准往前看，是否不紧跟着Lie字段</span>
<span class="token operator">/</span><span class="token punctuation">(</span><span class="token operator">?</span><span class="token operator"><</span><span class="token operator">!</span>Lie<span class="token punctuation">)</span>Jy<span class="token operator">/</span>g<span class="token punctuation">.</span><span class="token function">test</span><span class="token punctuation">(</span><span class="token string">'LieJy'</span><span class="token punctuation">)</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br></div></div><h3 id="require-content-匹配文件"><a href="#require-content-匹配文件" class="header-anchor">#</a> <code>require.content</code> 匹配文件</h3> <p>在 node.js 中常使用到 <code>require.content</code>动态获取文件，Frontender 在开发过程中也常有使用，如 vue.js 中常用 <code>require.content</code>来动态获取当前目录下的文件，免得每次手动引入的麻烦，于是一顿操作猛如虎~</p> <div class="language-js line-numbers-mode"><pre class="language-js"><code><span class="token comment">/*
目录结构：
|--languages
|----en.ts 英文字段
|----zh.ts 中文字段
|----index.ts 使用require.content整合字段，本文将不需被引用
*/</span>
<span class="token keyword">export</span> <span class="token keyword">default</span> <span class="token keyword">function</span> <span class="token function">loadLanguages</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token keyword">const</span> files <span class="token operator">=</span> require<span class="token punctuation">.</span><span class="token function">content</span><span class="token punctuation">(</span><span class="token string">'./'</span><span class="token punctuation">,</span> <span class="token boolean">false</span><span class="token punctuation">,</span> <span class="token regex"><span class="token regex-delimiter">/</span><span class="token regex-source language-regex">(?<!index)\.ts$</span><span class="token regex-delimiter">/</span></span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">const</span> language <span class="token operator">=</span> files<span class="token punctuation">.</span><span class="token function">keys</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">reduce</span><span class="token punctuation">(</span><span class="token punctuation">(</span><span class="token parameter">acc<span class="token punctuation">,</span> key</span><span class="token punctuation">)</span> <span class="token operator">=></span> <span class="token punctuation">{</span>
<span class="token keyword">const</span> name <span class="token operator">=</span> key<span class="token punctuation">.</span><span class="token function">replace</span><span class="token punctuation">(</span><span class="token regex"><span class="token regex-delimiter">/</span><span class="token regex-source language-regex">(.*\/)*([_-\w]+)(\.ts)*$</span><span class="token regex-delimiter">/</span></span><span class="token punctuation">,</span> <span class="token string">'$2'</span><span class="token punctuation">)</span> <span class="token operator">||</span> <span class="token string">''</span><span class="token punctuation">,</span>
message <span class="token operator">=</span> <span class="token function">files</span><span class="token punctuation">(</span>key<span class="token punctuation">)</span><span class="token punctuation">.</span>default<span class="token punctuation">;</span>
acc<span class="token punctuation">[</span>name<span class="token punctuation">]</span> <span class="token operator">=</span> message<span class="token punctuation">;</span>
<span class="token keyword">return</span> acc<span class="token punctuation">;</span>
<span class="token punctuation">}</span><span class="token punctuation">,</span> <span class="token punctuation">{</span><span class="token punctuation">}</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token function">loadLanguages</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 获取所有语言的字段</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br><span class="line-number">16</span><br><span class="line-number">17</span><br><span class="line-number">18</span><br></div></div><p>可见通过<code>/(?<!index)\.ts$/</code>即可排除<code>index.ts</code>的引用，؏؏☝ᖗ 乛 ◡ 乛 ᖘ☝؏؏</p> <h3 id="查找以某字符开头的字符串"><a href="#查找以某字符开头的字符串" class="header-anchor">#</a> 查找以某字符开头的字符串</h3> <div class="language-js line-numbers-mode"><pre class="language-js"><code><span class="token regex"><span class="token regex-delimiter">/</span><span class="token regex-source language-regex">^(?=JyLie).*$</span><span class="token regex-delimiter">/</span></span><span class="token punctuation">.</span><span class="token function">test</span><span class="token punctuation">(</span><span class="token string">'JyLie, Haha'</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// true</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br></div></div><h3 id="查找不以某字符开头的字符串"><a href="#查找不以某字符开头的字符串" class="header-anchor">#</a> 查找不以某字符开头的字符串</h3> <div class="language-js line-numbers-mode"><pre class="language-js"><code><span class="token regex"><span class="token regex-delimiter">/</span><span class="token regex-source language-regex">^(?!JyLie).*$</span><span class="token regex-delimiter">/</span></span><span class="token punctuation">.</span><span class="token function">test</span><span class="token punctuation">(</span><span class="token string">'Haha,JyLie'</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// true</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br></div></div><h3 id="查找以某字符结尾的字符串"><a href="#查找以某字符结尾的字符串" class="header-anchor">#</a> 查找以某字符结尾的字符串</h3> <div class="language-js line-numbers-mode"><pre class="language-js"><code><span class="token regex"><span class="token regex-delimiter">/</span><span class="token regex-source language-regex">^.*(?<=JyLie)$</span><span class="token regex-delimiter">/</span></span><span class="token punctuation">.</span><span class="token function">test</span><span class="token punctuation">(</span><span class="token string">'Haha, JyLie'</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// true</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br></div></div><h3 id="查找不以某字符结尾的字符串"><a href="#查找不以某字符结尾的字符串" class="header-anchor">#</a> 查找不以某字符结尾的字符串</h3> <div class="language-js line-numbers-mode"><pre class="language-js"><code><span class="token regex"><span class="token regex-delimiter">/</span><span class="token regex-source language-regex">^.*(?<!JyLie)$</span><span class="token regex-delimiter">/</span></span><span class="token punctuation">.</span><span class="token function">test</span><span class="token punctuation">(</span><span class="token string">'JyLie, Haha'</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// true</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br></div></div><h3 id="查找不包含某个字符的字符串"><a href="#查找不包含某个字符的字符串" class="header-anchor">#</a> 查找不包含某个字符的字符串</h3> <div class="language-js line-numbers-mode"><pre class="language-js"><code><span class="token regex"><span class="token regex-delimiter">/</span><span class="token regex-source language-regex">^(?!.*JyLie).*$</span><span class="token regex-delimiter">/</span></span><span class="token punctuation">.</span><span class="token function">test</span><span class="token punctuation">(</span><span class="token string">'hahah, JyLie, Haha'</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// false</span>
<span class="token operator">/</span><span class="token operator">^</span><span class="token punctuation">(</span><span class="token operator">?</span><span class="token operator">!</span><span class="token punctuation">.</span><span class="token operator">*</span>JyLie<span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token operator">*</span>$<span class="token operator">/</span><span class="token punctuation">.</span><span class="token function">test</span><span class="token punctuation">(</span><span class="token string">'JyLie, Haha'</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// false</span>
<span class="token operator">/</span><span class="token operator">^</span><span class="token punctuation">(</span><span class="token operator">?</span><span class="token operator">!</span><span class="token punctuation">.</span><span class="token operator">*</span>JyLie<span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token operator">*</span>$<span class="token operator">/</span><span class="token punctuation">.</span><span class="token function">test</span><span class="token punctuation">(</span><span class="token string">'hahah, JyLie'</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// false</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br></div></div><h3 id="查找指定字符之间不包含某个字符的字符串"><a href="#查找指定字符之间不包含某个字符的字符串" class="header-anchor">#</a> 查找指定字符之间不包含某个字符的字符串</h3> <div class="language-js line-numbers-mode"><pre class="language-js"><code><span class="token regex"><span class="token regex-delimiter">/</span><span class="token regex-source language-regex">A((?!JyLie).)+A</span><span class="token regex-delimiter">/</span></span><span class="token punctuation">.</span><span class="token function">test</span><span class="token punctuation">(</span><span class="token string">'hahah, JyLie, Haha '</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// false</span>
<span class="token operator">/</span><span class="token constant">A</span><span class="token punctuation">(</span><span class="token punctuation">(</span><span class="token operator">?</span><span class="token operator">!</span>JyLie<span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token punctuation">)</span><span class="token operator">+</span><span class="token constant">A</span><span class="token operator">/</span><span class="token punctuation">.</span><span class="token function">test</span><span class="token punctuation">(</span><span class="token string">'A hahah, JyLie, Haha A'</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// false</span>
<span class="token operator">/</span><span class="token constant">A</span><span class="token punctuation">(</span><span class="token punctuation">(</span><span class="token operator">?</span><span class="token operator">!</span>JyLie<span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token punctuation">)</span><span class="token operator">+</span><span class="token constant">A</span><span class="token operator">/</span><span class="token punctuation">.</span><span class="token function">test</span><span class="token punctuation">(</span><span class="token string">'A hahah, LieJy, Haha A'</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// true</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br></div></div><h2 id="结语"><a href="#结语" class="header-anchor">#</a> 结语</h2> <p>总的来讲，正则的断言就是要抓住以谁为基准对字符串做匹配，是以特定字符为基准<strong>往后</strong>匹配特定字符串呢，还是以特定字符为基准<strong>往前</strong>匹配特定字符串，搞清楚基准问题一切好办。</p> <p>啊哈哈哈哈嗝，刚加了个班总结文章，一眨眼就到 8 点半，是该归巢洗洗睡啦~</p> <h2 id="相关文献"><a href="#相关文献" class="header-anchor">#</a> 相关文献</h2> <ul><li><a href="https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Guide/Regular_Expressions/Assertions" target="_blank" rel="noopener noreferrer">MDN-JavaScript 正则断言<svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15" class="icon outbound"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path> <polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg></a></li></ul></div> <footer class="page-edit" style="display:none;"><!----> <!----></footer> <!----> <!----></main> <!----></div></div></div></div><div class="global-ui"><div class="back-to-ceiling" style="right:1rem;bottom:6rem;width:2.5rem;height:2.5rem;border-radius:.25rem;line-height:2.5rem;display:none;" data-v-a936bdb4 data-v-a936bdb4><svg t="1574745035067" viewBox="0 0 1024 1024" version="1.1" xmlns="http://www.w3.org/2000/svg" p-id="5404" class="icon" data-v-a936bdb4><path d="M526.60727968 10.90185116a27.675 27.675 0 0 0-29.21455937 0c-131.36607665 82.28402758-218.69155461 228.01873535-218.69155402 394.07834331a462.20625001 462.20625001 0 0 0 5.36959153 69.94390903c1.00431239 6.55289093-0.34802892 13.13561351-3.76865779 18.80351572-32.63518765 54.11355614-51.75690182 118.55860487-51.7569018 187.94566865a371.06718723 371.06718723 0 0 0 11.50484808 91.98906777c6.53300375 25.50556257 41.68394495 28.14064038 52.69160883 4.22606766 17.37162448-37.73630017 42.14135425-72.50938081 72.80769204-103.21549295 2.18761121 3.04276886 4.15646224 6.24463696 6.40373557 9.22774369a1871.4375 1871.4375 0 0 0 140.04691725 5.34970492 1866.36093723 1866.36093723 0 0 0 140.04691723-5.34970492c2.24727335-2.98310674 4.21612437-6.18497483 6.3937923-9.2178004 30.66633723 30.70611158 55.4360664 65.4791928 72.80769147 103.21549355 11.00766384 23.91457269 46.15860503 21.27949489 52.69160879-4.22606768a371.15156223 371.15156223 0 0 0 11.514792-91.99901164c0-69.36717486-19.13165746-133.82216804-51.75690182-187.92578088-3.42062944-5.66790279-4.76302748-12.26056868-3.76865837-18.80351632a462.20625001 462.20625001 0 0 0 5.36959269-69.943909c-0.00994388-166.08943902-87.32547796-311.81420293-218.6915546-394.09823051zM605.93803103 357.87693858a93.93749974 93.93749974 0 1 1-187.89594924 6.1e-7 93.93749974 93.93749974 0 0 1 187.89594924-6.1e-7z" p-id="5405" data-v-a936bdb4></path><path d="M429.50777625 765.63860547C429.50777625 803.39355007 466.44236686 1000.39046097 512.00932183 1000.39046097c45.56695499 0 82.4922232-197.00623328 82.5015456-234.7518555 0-37.75494459-36.9345906-68.35043303-82.4922232-68.34111062-45.57627738-0.00932239-82.52019037 30.59548842-82.51086798 68.34111062z" p-id="5406" data-v-a936bdb4></path></svg></div><div id="live2d-widget" class="live2d-widget-container" style="position:fixed;right:65px;bottom:0px;width:130px;height:290px;z-index:99999;opacity:0.8;pointer-events:none;"><canvas id="live2d_canvas" width="130" height="290" class="live2d_canvas" style="position:absolute;left:0px;top:0px;width:130px;height:290px;"></canvas></div></div></div>
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