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89 lines
2.8 KiB
HTML
89 lines
2.8 KiB
HTML
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<html>
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<head>
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<style type="text/css">
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.container {
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position: static;
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width: 800px;
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height: 350px;
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overflow: hidden;
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}
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.embed {
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height: 100%;
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width: 100%;
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min-width: 1000px;
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margin-left: -360px;
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margin-top: -57px;
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overflow: hidden;
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}
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body {
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width: 800px;
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margin: auto;
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padding: 1em;
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font-family: "Open Sans", sans-serif;
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line-height: 150%;
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letter-spacing: 0.1pt;
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}
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img {
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width: 90%;
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text-align: center;
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margin: auto;
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box-shadow: 0 4px 8px 0 rgba(0, 0, 0, 0.2), 0 6px 20px 0 rgba(0, 0, 0, 0.19);
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}
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pre, code {
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padding: 1em;
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}
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</style>
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<script>
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document.addEventListener('readystatechange', event => {
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if (event.target.readyState === "complete")
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document.activeElement.blur();
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</script>
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<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/highlight.js/9.18.1/styles/default.min.css">
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<script src="https://cdnjs.cloudflare.com/ajax/libs/highlight.js/9.18.1/highlight.min.js"></script>
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</head>
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<body>
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<h2 id="namedgroups">Named Groups</h2>
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<p>Regular expressions with lots of groups and backreferencing can be difficult to maintain, as adding or removing a capturing group in the middle of the regex turns to change the numbers of all the groups that follow the added or removed group.</p>
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<p>In regex, we have facility of named groups, which solves the above issue. Let's look at it.</p>
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<p>We can name a group by putting <code>?<name></code> just after opening the paranthesis representing a group. For example, <code>(?<year>\d{4})</code> is a named group.</p>
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<p>Below is a code, we have already looked in <strong>capturing groups</strong> part. You can see, the code is more readable now.</p>
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<pre><code class="js language-js">var str = "2020-01-20";
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// Pattern string
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var pattern = /(?<year>\d{4})-(?<month>\d{2})-(?<day>\d{2})/g;
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// Data replacement using $<group_name>
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var ans=str.replace(pattern, '$<day>-$<month>-$<year>');
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console.log(ans);
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// Output will be: 20-01-2020
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</code></pre>
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<p>Backreference syntax for numbered groups works for named capture groups as well. <code>\k<name></code> matches the string that was previously matched by the named capture group <code>name</code>, which is a standard way to backreference named group.</p>
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<div class="container">
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<iframe scrolling="no" style="position: absolute; top: -9999em; visibility: hidden;" onload="this.style.position='static'; this.style.visibility='visible';" src="https://regexr.com/4vu8k" class="embed"></iframe>
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</div>
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<script type="text/javascript">
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document.addEventListener('DOMContentLoaded', (event) => {
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document.querySelectorAll('pre code').forEach((block) => {
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hljs.highlightBlock(block);
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});
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});
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</script>
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</body>
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</html>
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