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<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8" />
<meta name="viewport" content="width=device-width, initial-scale=1, maximum-scale=1" />
<title>/Reg(exp){2}lained/</title>
<link href="../csss/slideshow.css" rel="stylesheet" />
<link href="../csss/reusable.css" rel="stylesheet" />
<link href="../talks/shared/intro-outro.css" rel="stylesheet" />
<link href="css/global.css" rel="stylesheet" />
<link href="css/theme.css" rel="stylesheet" />
<link href="css/talk.css" rel="stylesheet" />
<link href="css/regex-test.css" rel="stylesheet" />
</head>
<body>
<header id="intro" class="slide dont-resize">
<hgroup>
<h1>/Reg(exp){2}lained/</h1>
<h2>Demystifying regular expressions</h2>
</hgroup>
<p class="attribution">By Lea Verou (@LeaVerou)</p>
</header>
<section id="introduction">
<section id="hi" class="inverse slide dont-resize darker hi">
<figure class="delayed">
<img src="../talks/shared/img/me-pirate.png" alt="Picture of me" title="Pirate illustration by Lorenzo Grandi http://www.lorenzograndi.it/" />
<figcaption style="font-size: 240%">Привет, я Лиа</figcaption>
</figure>
</section>
<section class="inverse slide dont-resize darker hi" id="lesbian" data-steps="2">
<div>
<p class="funfact">#funfact</p>
<p>I grew up in Lesbos, Greece</p>
<p>…which technically makes me <strong>geographically Lesbian</strong></p>
</div>
</section>
<section class="top-heavy slide dont-resize" id="projects">
<ul class="plain">
<li><a href="http://mavo.io/" style="background-image: url(../talks/shared/img/project-mavo.png)">Mavo</a></li>
<li><a href="http://prismjs.com" style="background-image: url(../talks/shared/img/project-prism.png)">PrismJS</a></li>
<li><a href="http://leaverou.github.io/prefixfree" style="background-image: url(../talks/shared/img/project-prefixfree.png)">-prefix-free</a></li>
<li><a href="http://blissfuljs.com" style="background-image: url(../talks/shared/img/project-bliss.png)">Bliss</a></li>
<li><a href="http://css3test.com" style="background-image: url(../talks/shared/img/project-css3test.png)">css3test.com</a></li>
<li><a href="http://leaverou.github.io/awesomplete/" style="background-image: url(../talks/shared/img/project-awesomplete.png)">Awesomplete</a></li>
<li><a href="http://cubic-bezier.com/" style="background-image: url(../talks/shared/img/project-cubicbezier.png)">cubic-bezier.com</a></li>
<li><a href="http://dabblet.com" style="background-image: url(../talks/shared/img/project-dabblet.png)">dabblet.com</a></li>
<li><a href="http://leaverou.github.io/contrast-ratio/" style="background-image: url(../talks/shared/img/project-contrastratio.png)">Contrast Ratio</a></li>
</ul>
</section>
<section class="top-heavy image slide" id="csswg" data-credits="Daniel Glazman" data-steps="1">
<h1 class="caption">
<!-- <img src="../talks/shared/img/w3c.svg" alt="W3C" class="inline"> -->
W3C CSS Working Group Invited Expert
</h1>
<svg viewBox="0 0 100 100" class="annotation">
<ellipse />
</svg>
</section>
<section class="inverse slide dont-resize darker hi" id="book">
<a href="http://shop.oreilly.com/product/0636920031123.do">
<img src="../talks/shared/img/book.png" alt="CSS Secrets by O’Reilly" style="display:block" />
★★★★★ on Amazon
</a>
</section>
<article class="image slide" style="background: url(img/russian-csssecrets.jpg) center/contain no-repeat white">
</article>
<section class="top-heavy image slide" id="mit">
<h1><strong>2014 –</strong> Haystack Group, MIT CSAIL</h1>
</section>
</section>
<section class="slide dont-resize" id="names">
<div class="speech-bubble">
<ul>
<li>“Regular expression”</li>
<li>“Regexp”</li>
<li>“Regex”</li>
<li class="delayed invalid">“ASCII puke”</li>
</ul>
</div>
<div class="delayed speech-bubble">
<p><pre>/^Reg(exp?|ular expression)$/i</pre></p>
</div>
</section>
<article class="image slide" style="background-image: url(img/scaredcat.jpg)" title="Fear"></article>
<section class="image slide" style="background-image: url(img/strings.jpg)" data-source="http://www.flickr.com/photos/gargi/3010324017/">
<dl class="caption">
<dt>Regular expressions:</dt>
<dd>A way to describe a set of strings</dd>
</dl>
</section>
<section class="slide syntax-breakdown">
<h1><code style="font-size: 7vw;">
<span title="Starts with a slash">/</span>
<span title="Pattern (what to match)" data-index="1">&(lt|gt|amp);</span>
<span title="Ends with a slash">/</span>
<span title="Flags (combination of g, i, m, y, u, s)" data-index="1">gi</span>
</code></h1>
</section>
<section class="slide syntax-breakdown">
<h1><code style="font-size: 5.8vw;">/
<span title="Beginning of string">^</span>
Reg(ex
<span title="Maybe one p" data-index="1">p?</span>
<span title="or" data-index="1">|</span>
ular expression)
<span title="End of string">$</span>
/
<span title="Case insensitive" data-index="1">i</span>
</code></h1>
</section>
<section class="narrow slide">
<pre><code class="language-javascript">"pâté".normalize("NFD").replace(/[\u0300-\u036f]/g, "") // "pate"</code></pre>
<pre><code class="language-javascript">'lea@verou.me'.match(/(\w+)@/)[1] // "lea"</code></pre>
<pre><code class="language-javascript">code.replace(/ {4}/g, '\t'); // fix broken indentation</code></pre>
<pre><code class="language-markup"><input name="zip" pattern="\d{5}" /> </code></pre>
<p>Also: text editors, IDEs, command line tools (grep, etc), databases, and more</p>
</section>
<section>
<!-- <section class="slide" id="methods">
<h1>RegExp aware methods</h1>
<h2><code>RegExp.prototype</code></h2>
<ul>
<li><code class="language-javascript">test(String)</code></li>
<li><code class="language-javascript">exec(String)</code></li>
</ul>
<h2 style="margin-top: 1em"><code>String.prototype</code></h2>
<ul>
<li><code class="language-javascript">match(RegExp)</code></li>
<li><code class="language-javascript">replace(RegExp, String | Function)</code></li>
<li><code class="language-javascript">split(RegExp)</code></li>
<li><code class="language-javascript">search(RegExp)</code></li>
</ul>
</section> -->
<section class="slide" data-src="index.html" data-title="Try stuff out at regexplained.com"></section>
<section class="regex-test slide" data-pattern="a" title="Literals">
<h1>What we learned</h1>
<ul class="delayed-children persistent">
<li>Regexes match anywhere, unless restricted</li>
<li>Matches cannot intersect</li>
<li>Case sensitive by default, use the <code>i</code> flag to change</li>
<li>Unicode characters by <code>\uXXXX</code></li>
</ul>
<p class="hint">\u2665 for ♥, emojis, rainbow matches rainbow flag emoji</p>
</section>
<article class="slide" title="Flags">
<table>
<thead>
<th>Flag</th>
<th>Name</th>
<th>Purpose</th>
<th>ES?</th>
</thead>
<tr>
<td><code>g</code></td>
<td>Global</td>
<td>Get all matches</td>
<td>ES3</td>
</tr>
<tr>
<td><code>i</code></td>
<td>Case Insensitive</td>
<td>Ignore case when matching</td>
<td>ES3</td>
</tr>
<tr>
<td><code>m</code></td>
<td>Multiline</td>
<td><code>^</code> and <code>$</code> match the beginning and end of each line, not of the whole string</td>
<td>ES3</td>
</tr>
<tr>
<td><code>y</code></td>
<td>Sticky</td>
<td>Anchors each match of a regular expression to the end of the previous match.</td>
<td>ES2015</td>
</tr>
<tr>
<td><code>u</code></td>
<td>Unicode</td>
<td>Treat pattern as a sequence of unicode code points</td>
<td>ES2015</td>
</tr>
<tr>
<td><code>s</code></td>
<td>DotAll</td>
<td><code>.</code> matches newlines as well.</td>
<td>ES2018? (Stage 3)</td>
</tr>
</table>
</article>
<section class="regex-test slide" data-pattern="cat|bat|dog" data-test="cat" title="Grouping">
<h1>What we learned</h1>
<ul class="delayed-children persistent">
<li>| for alternatives</li>
<li>Group with parenthses (Useful for alternatives or quantifiers)</li>
<li>Alternatives can be empty</li>
<li>Order matters!</li>
</ul>
<p class="hint">(c|b|f|)at|dog, do(|g) for order</p>
</section>
<section class="slide" data-type="Challenge" data-duration="1" data-video="kitten.mp4" style="--position: right">
<h1>Test Challenge</h1>
<p>
<code>fizz</code>
<code>buzz</code>
<code>fizzbuzz</code>
</p>
</section>
<article class="narrow slide language-javascript" data-type="Solution">
<h1>Fizzbuzz</h1>
<pre><code>// Matches everything, including ""
/(fizz|)(buzz|)/</code></pre>
<pre class="delayed persistent"><code>// Correct but inelegant
/(fizzbuzz|fizz|buzz)/</code></pre>
<pre class="delayed persistent"><code>/(fizz(buzz|)|buzz)/</code></pre>
</article>
<!-- <section class="slide dont-resize" data-type="Challenge" data-duration="1" data-video="hamsters.webm" style="--position: right">
<h1>Font & Image MIME types</h1>
<p>
<code>image/png</code>
<code>image/jpeg</code>
<code>image/gif</code>
<code>font/ttf</code>
<code>font/otf</code>
<code>font/woff</code>
<code>font/woff2</code>
<span class="not">not</span> <code>image/ttf</code> <code>font/gif</code> etc
</p>
</section>
<section class="narrow slide language-javascript" data-type="Solution">
<h1 style="white-space: nowrap;">Font & Image MIME types</h1>
<pre><code>// Wrong! Matches image/ttf, font/gif etc
/(image|font)\/(png|jpeg|gif|ttf|otf|woff|woff2)/</code></pre>
<pre class="delayed persistent"><code>// Correct, but could be shorter
/image\/(png|jpeg|gif)|font\/ttf|otf|woff|woff2)/</code></pre>
<pre class="delayed persistent"><code>/image\/(png|jpeg|gif)|font\/(ttf|otf|woff(2|))/</code></pre>
<pre class="delayed persistent"><code>// Please don’t
/image\/(png|jpeg|gif)|font\/(t|o)tf|woff(|2))/</code></pre>
</section> -->
<section class="slide" data-type="Challenge" data-duration="2" data-video="hamsters.webm">
<h1>Emojis with woman</h1>
<p style="font-size: 200%;">
<code>👩</code>
<code>👩💼</code>
<code>👪</code>
<code>👨👩👦👦</code>
<code>👩👦👦</code>
<code>👩👧</code>
<code>👩👦</code>
<code>👩👩👦👦</code>
<code>👩👩👦</code>
<code>👩👩👧</code>
<code>💏</code>
<code>👩❤️💋👩</code>
<strong class="not">not</strong>
<code>👨👧</code>
<code>👨👨👧</code>
<code>👨👨👦</code>
<code>👨❤️👨</code>
</p>
</section>
<section class="narrow slide" data-type="Solution">
<h1>Emojis with woman</h1>
<pre><code class="language-javascript">// Ewww, just stop
/👩|👩💼|👪|👩👦👦|👩👧|👩👦|👩👩👦👦|👩👩👦|👩👩👧|👨👩👦👦|.../</code></pre>
<pre class="delayed persistent"><code class="language-javascript">/👩/ // Wrong, doesn’t include 👪 and 💏!</code></pre>
<pre class="delayed persistent"><code class="language-javascript">/👩|👪|💏/</code></pre>
</section>
<section class="regex-test slide" data-pattern="1.5" data-test="1.5" title="The dot metacharacter">
<p class="hint">/1.5/ show it matches 21056 etc, show two are needed to match emojis</p>
<h1>What we learned</h1>
<ul class="delayed-children persistent">
<li>Dot (.) matches anything, except line breaks</li>
<li>The experimental <code>s</code> flag makes it match line breaks</li>
<li>Escape metacharacters with a backslash</li>
</ul>
</section>
<section class="slide dont-resize" id="metacharacters">
<h1>The 12 metacharacters</h1>
<code>[</code>
<code>{</code>
<code>(</code>
<code>)</code>
<code>\</code>
<code>^</code>
<code>$</code>
<code>.</code>
<code>|</code>
<code>?</code>
<code>*</code>
<code>+</code>
</section>
<section class="regex-test slide" data-pattern="aaaaargh" title="Quantifiers">
<h1>What we learned</h1>
<ul class="delayed-children persistent">
<li>{n} = n times</li>
<li>{m,n} = at least m times but no more than n times</li>
<li>{m,} = at least m times</li>
</ul>
<p class="hint">(ab){n}, a{2,5} and caaaaaaaaaat, parentheses always needed for emoji</p>
</section>
<section class="regex-test slide" data-pattern="bo{0,}" data-test="boooo" title="Quantifier shortcuts">
<h1>What we learned</h1>
<ul class="delayed-children persistent">
<li>* = {0,} , + = {1,} , ? = {0,1}</li>
<li>Careful of accidental zero length matches!</li>
</ul>
</section>
<section class="regex-test slide" data-pattern="<.+>" data-test="<p>foo</p>" title="Greediness">
<h1>What we learned</h1>
<ul class="delayed-children persistent">
<li>Quantifiers are greedy</li>
<li>Lazify them by adding a ? after them</li>
</ul>
<p class="hint">Delete last > to show what happens</p>
</section>
<section class="regex-test slide" data-pattern="(b|d|f|g|l|m|p|r|t|y)uck" title="Character classes">
<h1>What we learned</h1>
<ul class="delayed-children persistent">
<li>Brackets = set, range or a combination of both</li>
<li>Concatenate multiple ranges for a union</li>
<li>Most metacharacters don’t need escaping in <code>[]</code></li>
</ul>
<p class="hint">in Unicode order</p>
</section>
<section class="slide" data-type="Challenge" data-duration="1" data-video="confused-kitten.webm">
<h1>Hex color</h1>
<p>
<code>#abc</code>, <code>#f00</code>, <code>#BADA55</code>, <code>#C0FFEE</code>
</p>
</section>
<section class="narrow slide" data-type="Solution">
<h1>Hex color</h1>
<pre><code class="language-javascript">/#[a-f0-9]{3,6}/i // Wrong!</code></pre>
<pre class="delayed persistent"><code class="language-javascript">/#([a-f0-9]{3}){1,2}/i</code></pre>
</section>
<section class="regex-test slide" data-pattern="[a-zA-Z0-9_]" title="Predefined character classes">
<h1>What we learned</h1>
<ul class="delayed-children persistent">
<li>
<code>\w</code> = <code>[a-zA-Z0-9_]</code>,
<code>\d</code> = <code>[0-9]</code>,
<code>\s</code> ≈ <code>[\t\r\n ]</code></li>
<li>Combine to form more complex character classes</li>
</ul>
</section>
<section class="slide" data-type="Example">
<h1>Counting words (roughly)</h1>
<pre><code class="language-javascript">function wordCount(text){
return text.match(/\w+/g).length;
}</code></pre>
<pre><code class="language-javascript">function wordCount(text){
return text.split(/\s+/).length;
}</code></pre>
</section>
<section class="slide" data-type="Challenge" data-duration="2" data-video="racoon.webm">
<h1>Number</h1>
<p>Without exponent or digit separators</p>
<p>
<code>-1</code> <code>.05</code> <code>+1000</code> <code>3.1415926535</code> <code>42.</code>
</p>
</section>
<section class="narrow slide" data-type="Solution">
<h1>Number</h1>
<pre><code class="language-javascript">/^[-+]?[\d.]+$/ // Too lax</code></pre>
<pre class="delayed persistent"><code class="language-javascript">/^[-+]?\d*\.?\d+$/ // False negatives: 5.</code></pre>
<pre class="delayed persistent"><code class="language-javascript">/^[-+]?\d*\.?\d*$/ // False positives: ., +., + etc</code></pre>
<pre class="delayed persistent"><code class="language-javascript">// Accurate, but is it worth it?
/^[-+]?(\d*\.?\d+|\d+\.)$/</code></pre>
</section>
<section class="regex-test slide" data-pattern="[\u0001-/:-@[-^`{-\uffff]" data-test="afz" title="Negated character classes">
<!-- [\u0001-/:-@[-^`{-\uffff] = \W -->
<h1>What we learned</h1>
<ul class="delayed-children persistent">
<li><code>^</code> negates a character class</li>
<li>
<code>\W</code> = <code>[^\w]</code>,
<code>\D</code> = <code>[^\d]</code>,
<code>\S</code> = <code>[^\s]</code>
</li>
<li>Even the dot is a character class: <code>.</code> = <code>[^\r\n\u2028\u2029]</code></li>
<li>DotAll alternatives: <code>[^]</code>, <code>[\S\s]</code>, <code>[\W\w]</code>, <code>[\D\d]</code></li>
</ul>
</section>
<section class="slide" data-type="Example">
<h1>Strip HTML</h1>
<pre><code class="language-javascript">function stripHTML(str){
return str.replace(/<.+?>/g, '');
}</code></pre>
<pre class="delayed"><code class="language-javascript">function stripHTML(str){
return str.replace(/<[^>]+>/g, '');
}</code></pre>
<p>Warning: Will fail in edge cases</p>
</section>
<section class="slide" data-type="Challenge" data-duration="1" data-video="munchkin.mp4">
<h1>Credit card numbers</h1>
<p>
<code>4060 1234 5678 9000</code>
<code>4060-1234-5678-3457</code>
<code>1230123456789123</code>
<code>4.060/123456-78 90-00</code>
<strong class="not">not</strong>
<code>hello</code>
<code>4060</code>
<code>12345678901234567890</code>
</p>
</section>
<section class="narrow slide" data-type="Solution">
<h1>Credit card numbers</h1>
<pre><code class="language-javascript">// Never do this!
/\d{16}/</code></pre>
<pre class="delayed persistent"><code class="language-javascript">// Limited grouping + allows 19 digit numbers
/(\d{4}.?){3}\d{4}/</code></pre>
<pre class="delayed persistent"><code class="language-javascript">/(\d\D*){16}/</code></pre>
</section>
<section class="regex-test slide" data-pattern="\p{Script=Cyrillic}+" data-test="Веру Лиа" data-flags="gu" title="Unicode Property Escapes">
<h1>What we learned</h1>
<ul class="delayed-children persistent">
<li>Syntax: <code>\p{<em>UNICODE_PROPERTY</em>=<em>VALUE</em>}</code>. Needs <code>u</code> flag.</li>
<li>When Unicode Property is <code>General_Category</code> it can be omitted.</li>
<li>Experimental, <a href="https://github.com/tc39/proposal-regexp-unicode-property-escapes">proposal in Stage 3</a>, implemented in Chrome & Safari</li>
</ul>
<p class="hint">Script=Cyrillic</p>
</section>
<section class="regex-test slide" data-pattern="(Java|ECMA)Script" data-test="JavaScript" title="Capturing">
<h1>What we learned</h1>
<ul class="delayed-children persistent">
<li>Parentheses form capturing groups</li>
<li>Add <code>?:</code> in the begninning to avoid this</li>
</ul>
</section>
<section class="regex-test slide" data-pattern="^a" data-test="cat" title="Anchors">
<h1>What we learned</h1>
<ul class="delayed-children persistent">
<li><code>^</code> = beginning of string</li>
<li><code>$</code> = end of string</li>
<li>beginning/end of lines, with the <code>m</code> flag</li>
</ul>
</section>
<section class="slide" data-type="Challenge" data-duration="2" data-video="goats.webm">
<h1>ISO 8601 Dates</h1>
<p>Just dates, no time or timezone information</p>
<p>
<code>2012-12-12</code>, <code>1986-06-13</code>
</p>
</section>
<section class="slide" data-type="Solution">
<h1>ISO 8601 Dates</h1>
<pre><code class="language-javascript">/^\d{4}-\d{2}-\d{2}$/.test(str)</code></pre>
<pre class="delayed persistent"><code class="language-javascript">/^\d{4}-(0\d|1[0-2])-([0-2]\d|3[01])$/.test(s)</code></pre>
<p class="delayed">Can it be improved further?</p>
</section>
<section class="slide" data-type="Example">
<h1>Trimming a string</h1>
<pre><code class="language-javascript">if (!String.prototype.trim) {
String.prototype.trim = function(){
return this.replace(/^\s+|\s+$/g, '');
}
}</code></pre>
</section>
<section class="regex-test slide" data-pattern="\b" title="Assertions">
<h1>What we learned</h1>
<ul class="delayed-children persistent">
<li>Assertions are zero width</li>
<li><code>\b</code> = word boundary = between <code>\w</code> and <code>\W|^|$</code></li>
<li><code>\B</code> = non-word boundary = between <code>\w</code> and <code>\w</code> or <code>\W</code> and <code>\W</code></li>
</ul>
</section>
<!-- <article class=" slide language-js">
<h1>Before <code>element.classList</code>…</h1>
<pre><code>function removeClass(element, name) {
var regex = RegExp("\\b" + name + "\\b", "g");
return element.className = element.className.replace(regex, ""));
}</code></pre>
<pre class="delayed"><code>element.className = "item-toolbar";
removeClass(element, "toolbar"); // "item-"</code></pre>
</article> -->
<section class="regex-test slide" data-pattern="a(b)" data-test="ab" title="Lookahead">
<h1>What we learned</h1>
<ul class="delayed-children persistent">
<li><code>(?=a)</code> = followed by a, which can be any regex</li>
<li><code>(?!a)</code> = NOT followed by a</li>
</ul>
</section>
<section id="lookahead-hacks" class="language-javascript">
<header class="slide">
<h1>Lookahead hacks</h1>
<h2>for fun and profit</h2>
</header>
<section class="slide">
<h1>Intersection <span class="math"><em>A</em> ∩ <em>B</em></span></h1>
<p>“Password must be 6 letters or longer, and must contain at least one number, one letter, and one symbol.”</p>
<pre><code>password.length > 6
&& /\d/.test(password) // has digit?
&& /[a-z]/i.test(password) // has letter?
&& /\W/.test(password) // has symbol?</code></pre>
<pre class="delayed"><code>// Or, with lookaheads…
/^(?=.*\d)(?=.*[a-z])(?=.*[\W_]).{6,}$/i</code></pre>
</section>
<section class="slide">
<h1>Subtraction <span class="math"><em>A</em> – <em>B</em></h1>
<p>“Any integer that’s NOT divisible by 50”</p>
<pre><code> /^(?!\d+[50]0)\d+$/</code></pre>
</section>
<section class="slide">
<h1>Negation <span class="math"><em>A̅</em></h1>
<p>“Anything that doesn’t contain "foo"”</p>
<pre><code>/^(?!.*foo).+$/</code></pre>
</section>
</section>
<section class="regex-test slide" data-pattern="(?<=a)b" data-test="ab" title="Lookbehind">
<h1>What we learned</h1>
<ul class="delayed-children persistent">
<li><code>(?<=a)</code> = preceded by a, which can be any regex</li>
<li><code>(?<!a)</code> = NOT preceded by a</li>
<li>Experimental (<a href="https://github.com/tc39/proposal-regexp-lookbehind">Proposal in Stage 3</a>), only supported in V8 behind a flag</li>
</ul>
</section>
<section class="regex-test slide" data-pattern="('|").+?('|")" title="Backreferences">
<h1>What we learned</h1>
<ul class="delayed-children persistent">
<li><code>\N</code> = Nth backreference</li>
</ul>
<p class="hint">('|")(\\\1|.)+?\1 for escaped quotes</p>
</section>
<section class="regex-test slide" title="Account for escaped quotes AND backslashes"
data-pattern="("|')(\\?.)*?\1"
data-test='"He 'said' \"hi\"!" "another string"'>
<p class="credit">Regex credit: Steven Levithan</p>
</section>
<section class="slide" data-type="Challenge" data-duration="2" data-video="maru.webm">
<h1>Correctly Nested Parens</h1>
<p>
<code>()</code>, <code>(())()</code>, <code>(()()())</code>, <code>((((((()))))))</code>
<strong class="not">not</strong> <code>()(</code>, <code>)</code>, <code>((((((()))</code>
</p>
</section>
<article class="top-heavy image slide" id="troll">
<h1 class="delayed">Not a regular language</h1>
</article>
<article class="slide" id="cfg">
<h1>Context Free Grammar</h1>
<ul class="plain math">
<li><em>S</em> → (<em>S</em>)</li>
<li><em>S</em> → <em>S</em><em>S</em></li>
<li><em>S</em> → <em>ε</em></li>
</ul>
</article>
</section>
<section>
<header class="slide" id="best-practices">
<h1>Best Practices</h1>
</header>
<section class="image slide" id="precise-impractical" data-source="regular-expressions.info/email.html">
<code>(?:[a-z0-9!#$%&'*+/=?^_`{|}~-]+(?:\.[a-z0-9!#$%&'*+/=?^_`{|}~-]+)*|"(?:[\x01-\x08\x0b\x0c\x0e-\x1f\x21\x23-\x5b\x5d-\x7f]|\\[\x01-\x09\x0b\x0c\x0e-\x7f])*")@(?:(?:[a-z0-9](?:[a-z0-9-]*[a-z0-9])?\.)+[a-z0-9](?:[a-z0-9-]*[a-z0-9])?|\[(?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?|[a-z0-9-]*[a-z0-9]:(?:[\x01-\x08\x0b\x0c\x0e-\x1f\x21-\x5a\x53-\x7f]|\\[\x01-\x09\x0b\x0c\x0e-\x7f])+)\])</code>
<h1 class="caption">Practicality > Precision</h1>
</section>
<section class="narrow slide" style="min-width: 20em">
<h1>Email</h1>
<pre><code class="language-javascript">// Don’t ever do this
/^[a-z]+@[a-z]+\.[a-z]{2,5}/</code></pre>
<p class="match-examples delayed persistent">
<code>lea@verou.me</code>
<code>leaverou@mit.edu</code>
<code>foo@google.co.jp</code>
<code>Лиа@Веру.рф</code>
<code>λία@βέρου.ελ</code>
<code>me@lea.moscow</code>
</p>
<pre class="delayed persistent"><code class="language-javascript">// Yes, it’s ok to be lax!
/^\S+@\S+\.\S+/</code></pre>
</section>
<section class="top-heavy image slide" style="background-image: url(img/pregnancy-test.jpg);" data-source="http://www.flickr.com/photos/mandaloo/4369363690/">
<h1>False positives vs false negatives</h1>
</section>
<section class="image slide language-javascript" id="kiss">
<div class="caption">
<h1>Keep it simple</h1>
<h2>Even if it means not using regexes at all</h2>
</div>
<ul class="plain delayed-children js-vs-regex">
<li>
<code>str === "foo"</code>
<strong>></strong>
<code>/^foo$/.test(str)</code>
</li>
<li>
<code>str.indexOf("foo") > -1</code>
<strong>></strong>
<code>/foo/.test(str)</code>
</li>
<li>
<code>str.indexOf("foo") === 0</code>
<strong>></strong>
<code>/^foo/.test(str)</code>
</li>
</ul>
</section>
<section class="slide">
<h1>For performance</h1>
<ul>
<li>Avoid greedy quantifiers</li>
<li>Don’t forget anchors (<code>^</code> and <code>$</code>)</li>
<li>Be as specific as possible</li>
<li>Prefer non-capturing groups <code>(?:)</code></li>
<li>Minimize backtracking</li>
</ul>
</section>
<section class="regex-test slide" data-pattern="(x+x+)+y" data-test="xxxx" title="Catastrophic backtracking">
<h1>What we learned</h1>
<ul class="delayed-children persistent">
<li>Only applies when there is no match</li>
<li>Avoid nested quantifiers</li>
</ul>
</section>
</section>
<!-- <section>
<header class="slide" id="js-regexp-api">
<h1>JS RegExp API</h1>
</header>
<section class="slide">
<h1>RegExp instances</h1>
<pre><code class="language-javascript">var literal = /^\$\d+/g,
// You don’t need the new operator
dynamic = RegExp('^\\$\\d+', 'g');</code></pre>
<ul class="delayed">
<li>Literals are simpler, faster, more concise</li>
<li>Only use the constructor when you really have to!</li>
</ul>
</section>
<section class="slide">
<h1>RegExp properties for flags</h1>
<ul>
<li>
<code>RegExp#global</code>
</li>
<li>
<code>RegExp#multiline</code>
</li>
<li>
<code>RegExp#ignoreCase</code>
</li>
</ul>
<pre><code class="language-javascript">>>> /a/g.global; // true
>>> /a/.global; // false
>>> /a/m.multiline; // true
>>> /a/gi.multiline; // false
>>> /a/i.ignoreCase; // true</code></pre>
</section>
<section class="slide">
<h1>Other RegExp properties</h1>
<ul>
<li>
<code>RegExp#source</code>
<pre><code class="language-javascript">console.log(/a/i.source) // "a"</code></pre>
</li>
<li><code>RegExp#lastIndex</code></li>
</ul>
</section>
<section class="slide" data-import="methods"></section>
<section class="slide">
<h1><code>RegExp#test</code></h1>
<pre><code class="language-javascript">/a/.test('ab'); // returns true</code></pre>
<ul>
<li>Faster than most of the others</li>
</ul>
</section>
<section class="slide">
<h1><code>RegExp#exec</code></h1>
<pre><code class="language-javascript">/a(b)/.exec('abba'); // ["ab", "b"]</code></pre>
<pre class="delayed"><code class="language-javascript">var reg = /a(b)/g, bar = 'abba', matches = [], m;
while (m = reg.exec(bar))
matches.push({
index: m.index, // reg.lastIndex-m[0].length+1
length: m[0].length,
groups: m
});</code></pre>
</section>
<section class="slide">
<h1><code>RegExp#exec</code></h1>
<pre><code class="language-javascript">>>> /a(bc)/.exec('abcba')[1];
"bc"</code></pre>
<pre><code class="language-javascript">>>> /a(bc)/.exec('abba')[1];</code>
<code class="error">TypeError: Cannot read property '1' of null</code></pre>
<div class="delayed">
<p>Handy trick by James Padolsey:</p>
<pre><code class="language-javascript">>>> (/regex/.exec('string') || [,''])[1];</code></pre>
</div>
</section>
<section class="slide">
<h1><code>String#match</code></h1>
<pre><code class="language-javascript">>>> 'abcdef'.match(/(\w){3}/);
["abc", "c"] // Same as /(\w){3}/.exec('abcdef')</code></pre>
<pre><code class="language-javascript">>>> 'abcdef'.match(/(\w){3}/g);
["abc", "def"]</code></pre>
<pre><code class="language-javascript">>>> 'ab'.match(/(\w){3}/g);
null</code></pre>
</section>
<section class="slide">
<h1><code>String#replace</code></h1>
<pre><code class="language-javascript">>>> 'blabla'.replace('b', ''); // "labla"</code></pre>
<pre class="delayed persistent"><code class="language-javascript">>>> 'blabla'.replace(/b/g, ''); // "lala"</code></pre>
<pre class="delayed persistent"><code class="language-javascript">>>> 'blabla'.replace(/(\w)/g, '$1$1'); // "bbllaabbllaa"</code></pre>
<pre class="delayed persistent"><code class="language-javascript">>>> 'border-radius'.replace(/-(\w)/g, function($0,$1){
return $1.toUpperCase();
}); // "borderRadius"</code></pre>
</section>
<section class="slide">
<h1><code>String#split</code></h1>
<pre><code class="language-javascript">'Lea wants a $20K Mini.'.split(/\s+/).length; // 5</code></pre>
<h1><code>String#search</code></h1>
<pre><code class="language-javascript">'Lea wants a $20K Mini.'.search(/\s+/); // 3</code></pre>
<ul class="delayed">
<li>Like a regex-aware <code>String#indexOf</code>!</li>
</ul>
</section>
</section> -->
<!-- <section>
<header class="slide" id="tools">
<h1>Tools</h1>
</header>
<section class="slide">
<hgroup>
<h1>XRegExp</h1>
<h2>By Steven Levithan</h2>
</hgroup>
<p>RegExp wrapper that adds awesomeness like:</p>
<ul>
<li>Comments in regexes</li>
<li>Flag to turn off automatic capturing</li>
<li>Flag to ignore whitespace</li>
<li>Named capturing groups</li>
<li>Unicode-aware predefined classes</li>
<li>Smooths out browser bugs</li>
<li>Plugins for even more awesomeness</li>
</ul>
</section>
<section class="slide" data-src="http://xregexp.com/"></section>
<section class="slide">
<hgroup>
<h1>Regexpal</h1>
<h2>By Steven Levithan</h2>
</hgroup>
<p>Simple but powerful regexp tester</p>
<ul>
<li>Highlights regex syntax and matches as you type</li>
<li>Includes a quick reference for regex syntax</li>
<li>Knows about syntax that doesn’t work correctly in some browsers, and marks it as an error</li>
<li>Pure JavaScript, so you can save it and use offline</li>
</ul>
</section>
<section class="slide" data-src="http://regexpal.com/"></section>
<section class="slide" data-src="http://www.regexbuddy.com/"></section>
<section class="slide">
<h1>Resources</h1>
<h2>Online:</h2>
<ul style="word-break: break-all;">
<li><a href="http://www.regular-expressions.info">regular-expressions.info</a></li>
<li><a href="http://blog.stevenlevithan.com/">blog.stevenlevithan.com</a>
<li><a href="https://developer.mozilla.org/en/JavaScript/Guide/Regular_Expressions">developer.mozilla.org/en/JavaScript/Guide/Regular_Expressions</a></li>
</ul>
<h2>Books:</h2>
<ul>
<li>Regular Expressions Cookbook - Jan Goyvaerts & Steven Levithan</li>
<li>Mastering Regular Expressions - Jeffrey E.F. Friedl</li>
</ul>
</section>
</section> -->
<article class="slide" id="video-credits">
<h1>Video Credits</h1>
<ul class="plain">
<li><a href="https://www.youtube.com/watch?v=IwtdIXWGry4">Melanie Raccoon riding bike-side angle</a></li>
<li><a href="https://twitter.com/AMAZlNGNATURE/status/938663598263484416">Living the dream</a></li>
<li><a href="https://www.youtube.com/watch?v=mt084vYqbnY">Hamster Has Epic Fail on Running Wheel</a></li>
<li><a href="https://www.youtube.com/watch?v=RN50R3gycgo&feature=youtu.be&t=7">Goat Kid Pajama Party</a></li>
<li><a href="https://www.youtube.com/watch?v=xdhLQCYQ-nQ">大きな箱とねこ。</a></li>
<li><a href="https://twitter.com/videocats/status/940154890004942848">Shiba Munchkin</a></li>
<li><a href="https://www.youtube.com/watch?v=HECa3bAFAYk">Fluffy kitten is confused</a></li>
<li><a href="https://twitter.com/videocats/status/938482862680133632">Learning to drink</a></li>
</ul>
</article>
<article class="slide" id="thankyou" title="Thank you!" data-credits="gifimage.net, giphy.com"></article>
<footer class="slide dont-resize">
<img src="../talks/shared/img/mark.svg" class="logo" />
<h1>Спасибо!</h1>
<img src="../talks/css-variables/img/stickers.jpg" class="stickers delayed" alt="">
<p class="stickercaption delayed">Want one? Just ask!---></p>
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<li style="--icon: '🌍'"><a href="http://mavo.io">lea.verou.me</a></li>
<li style="--icon: '✉'"><a href="mailto:lea@verou.me">lea@verou.me</a></li>
<li style="--icon: '🐦'"><a href="http://twitter.com/leaverou">@leaverou</a></li>
</ul>
<p>Slides: <a href="https://leaverou.github.io/regexplained/slides.html">leaverou.github.io/regexplained/slides.html</a></p>
<p style="font-size: 50%;">This slide deck was entirely built with open web technologies! Slideshow framework: <a href="http://github.com/LeaVerou/CSSS">github.com/LeaVerou/CSSS</a></p>
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