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How do I set the load and execution order of two external async Javascript files?
Given the following...
<script src="framework.js" async></script> // Larger file
<script src="scripts.js" async></script> // Small file
Though second in order scripts.js is downloading and executing before framework.js due to it's file size, but scripts.js is dependent on framework.js.
Is there a way natively to specify the load and execution order whilst still maintaining async properties?
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write before the document has loaded, the script will be executed synchronously as part of loading the page, and will not include any asynchronous callback behavior on its own. If you're creating a script element and adding it to the page, then you'll have access to add event listeners to trigger asynchronously.
onload will wait for those asynchronous scripts to finish loading.
Asynchronous loading means that the code will be processed simultaneously with the rest of the page's content. In other words, the browser will have no downtime while loading a page as it will keep working while waiting for the request to be handled and the code executed in the background.
You want to use defer if you want to preserve the execution order. What defer does is it async downloads the script, but defers execution till html parsing is done.
<script src="framework.js" defer></script>
<script src="scripts.js" defer></script>
However, you may want to start creating custom bundles once the number of scripts go higher.
You can see the difference here
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If you need a solution for IE9 (since it does not support the defer attribute), I have created a small loader script:
https://github.com/mudroljub/js-async-loader
It loads all your scripts asynchronously and then executes them in order.
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