ready

A pattern to bootstrap any JavaScript on DOMContentLoaded.

Live test.

the pattern

<!-- add these 2 script on top of every page * -->
<!-- * these MUST be two separate scripts! -->
<script>this.Promise||document.write('<script src="//cdn.jsdelivr.net/npm/es6-promise/dist/es6-promise.auto.min.js"><\x2fscript>')</script>
<script>this.ready=new Promise(function($){document.addEventListener('DOMContentLoaded',$,{once:true})})</script>
<!-- so that every other script after can simply use ready.then(...) to bootstrap -->
<script>
// proof of concept @ https://webreflection.github.io/ready/
ready.then(function () {
  document.body.innerHTML = 'Yeah, the <a href="https://github.com/WebReflection/ready">ready</a> pattern works!';
});
</script>

in a nutshell

• all browsers with native Promise support won't ever use document.write
• all browser that don't have native Promise won't ever have issues with document.write
• the two different <script> tags grant the correct execution order
• the {once:true} third argument ensures in modern browsers the listener is cleaned up ASAP and in older browsers it grants that there is a third argument
• the this.ready= is used, instead of a quirky ready=, to ensure if your project does some sort of linting/variables leaking validation it wouldn't bother that script.
• every browser can now use a single global ready promise to bootstrap

why

In September 2015 there was an attempt to bring document.ready to every browser.

Philosophy took over, so that in October 2016 there was a follow up attempt to bring document.{parsed,contentLoaded,loaded} promises to every browsers.

That resulted into pretty much nothing for 3 years, that's why.

improvements ?

• if you are targeting modern browsers you can fully remove the first script.
• if in 2039 they'll ship a global ready you can refactor your code via grep ready.then
• shortcut targeting modern browsers only (Edge, Chrome, Safari, Firefox, others)

<script>this.ready=new Promise($=>addEventListener('DOMContentLoaded',$,{once:!0}))</script>

You read that correctly, the DOMContentLoaded event reaches the global window too.

license ?

You can do whatever you want with this pattern, I haven't invented anything.

However, be sure the used Promise polyfill license is compatible with your project.

The proposed es6-promise one uses a MIT License.