How to defer inline Javascript?
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<span>2020-11-28 23:42</span>
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<h2>Defer/async script tags are not good enough</h2>
<p>There is a common knowledge that you should use <code><script src=".." async defer></code> (or set <code>script.async = true</code> before assigning <code>src</code>, when you do it from JS) and/or put your scripts at the very bottom of the page, so that as much as possible of the page gets loaded and rendered to the user, as fast as possible.</p>
<p>defer.js (note: <strong>I am the author of this script</strong>) is written in plain JavaScript, making lazy-loading other contents more fast and performant. You can defer any javascript files as well as inline script blocks efficiently.</p>
<p><img src="https://raw.githubusercontent.com/shinsenter/defer.js/master/docs/assets/defer-script.jpg" alt="Defer loading of JavaScript"></p>
<p>If your page is just an HTML page enhanced with some JavaScript, then you're good with just <code><script async></code>. It takes time for browser to parse and execute those scripts, and each UI change may reflow your layout, make your load speed more slow, no one likes staring at a blank white page; users are impatient and will leave quickly.</p>
<p>In various cases, using <code>async</code> or <code>defer</code> does not deliver faster page speed than defer.js does.</p>
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<p>From MDN docs: </p>
<blockquote>
<p><strong>defer</strong><br>
This Boolean attribute is set to indicate to a browser that the script is meant to be executed after the document has been parsed, but before firing <code>DOMContentLoaded</code>. <strong><em>The defer attribute should only be used on external scripts.</em></strong> </p>
</blockquote>
<p>This is called an IIFE <em>(Immediately Invoked Function Expression)</em> which gets executed before DOM is available. So, in that case <code>jQuery</code> is undefined because it it not in the DOM. </p>
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<span>2020-11-28 23:53</span>
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<p>You can create a Base64 URL out of the script and put it into the src!</p>
<pre><code><script src="data:text/javascript;base64,YWxlcnQoJ0hlbGxvIHdvcmxkIScpOw=="
defer>
</script>
</code></pre>
<p>I built a quick test to see it in action.
You should see an alert with <code>Hello world!</code> last if <code>defer</code> is working:</p>
<p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
<div class="snippet-code">
<pre class="snippet-code-html lang-html prettyprint-override"><code><script defer>
alert('Why no defer?!?');
</script>
<!-- alert('Hello world!'); -->
<script src="data:text/javascript;base64,YWxlcnQoJ0hlbGxvIHdvcmxkIScpOw=="
defer></script>
<script>
alert('Buh-bye world!');
</script></code></pre>
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<p>Doing it manually is a little laborious so if you have the luxury of compiling your HTML in some way (Handlebars, Angular, etc.) then that helps a lot.</p>
<p>I'm currently using:</p>
<pre><code><script src="data:text/javascript;base64,{{base64 "alert('Hello world!');"}}"
defer>
</script>
</code></pre>
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<span>2020-11-28 23:56</span>
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<h1>defer loading with plain text Data URI - Chrome and FF</h1>
<p>#noLib #vanillaJS</p>
<p><strong>suggest not to use on Cross Browser PRODuction</strong> </p>
<p>until MS IE dies and MS Edge will adopt the Chromium open source ;)</p>
<h2>the only way to defer script is <strong>external file</strong> or <strong>Data_URI</strong> (without using event DOMContentLoaded)</h2>
<h3>defer</h3>
<p>spec script#attr-defer (MDN web docs): "This attribute must not be used if the src attribute is absent (i.e. for inline scripts), in this case it would have no effect.)"</p>
<h3>Data_URI</h3>
<p>spec Data_URI</p>
<p>with right <strong>type "text/javascript"</strong> there is no need to <strong>base64</strong> at all... ;) </p>
<p><strong>using plain text</strong> so you can use simple:</p>
<pre><code><script defer src="data:text/javascript,
//do something with b-lazy plugin, lightbox plugin and then with flexslider
lightbox.option({
resizeDuration: 200,
wrapAround: true
})
">
</code></pre>
<p>yes, it's little bit weird hack, but <code><script type="module"></code> are deferred by default, there is no other option to <strong>mix following in exact order</strong>:</p>
<ul>
<li>module external files - deferred <strong>by default</strong></li>
<li>module inline scripts - deferred <strong>by default</strong></li>
<li>external files - <strong>optionally</strong> deferred</li>
<li>inline scripts - only with this <strong>hack</strong> - as I know (without libraries/frameworks)</li>
</ul>
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<p>The scripts with the <code>defer</code> attribute load in the order they are specified, but <em>not before</em> the document itself has been loaded. As <code>defer</code> has no effect on <code>script</code> tags unless they also have the <code>src</code> attribute, the first script that gets executed is your inline script. So at that time jQuery is not loaded yet.</p>
<p>You can solve this in at least two ways:</p>
<ul>
<li><p>Put your inline script in a <code>.js</code> file and reference it with a <code>src</code> attribute (in addition to the <code>defer</code> attribute which you already had there), or</p></li>
<li><p>Let your inline script wait for the document and the deferred scripts to be loaded. The <code>DOMContentLoaded</code> event will fire when that has happened:</p>
<pre><code><script>
window.addEventListener('DOMContentLoaded', function() {
(function($) {
//do something with b-lazy plugin, lightbox plugin and then with flexslider
})(jQuery);
});
</script>
</code></pre></li>
</ul>
<p>NB: Notice that in the latter case <code>$(document).ready(function()</code> is not included any more, as that would wait for the same event (<code>DOMContentLoaded</code>). You <em>could</em> still include it like you had in your original code, but then jQuery would just execute the callback <em>immediately</em>, which makes no practical difference.</p>
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