HTML and CSS Reference
In-Depth Information
In addition to async , you're very likely to see more scripts that are dependent on other scripts. You could be
referencing an external library or another dependency, like page content, that's present before the ad executes. You
can use a new JavaScript attribute called defer , which instructs the DOM parser to load scripts in the order they're
interpreted. For example, you may want to load a larger deferred script before loading another script that references
the previous one. Using the defer attribute more often, you'll notice fewer errors when dealing with the sequencing of
script files. Listing 3-5 outlines how to use the defer attribute.
Listing 3-5. Using JavaScript's defer Attribute
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<script defer src=' ' ></script>
<script defer src=' http://code.two.js ' ></script>
<script defer src=' http://code.three.js ' ></script>
<script defer src=' http://code.four.js ' ></script>
Keep in mind neither async nor defer blocks the DOM parser, resulting in a better experience for users viewing
the page content. It also goes to mention that defer occurs before the DOMContentLoaded event from the browser.
HTML5 welcomes users with a requestAnimationFrame for dealing with JavaScript animation, versus the old way of
using setTimeout or setInterval . Use of requestAnimationFrame explicitly tells the browser what your intentions
are for animation. Traditionally, developers used the code shown in Listing 3-6 for moving something on the page.
Listing 3-6. JavaScript setInterval
window.setInterval(function() {
//move and repeat.
}, 1000 / 60); // 60fps.
Now, we can use requestAnimationFrame , as shown in Listing 3-7.
Listing 3-7. Using requestAnimationFrame
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
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