I have defined a custom element and I want to execute a script only when the custom element is upgraded to its registered type. The use case is that I must call a custom method.
My main html file looks like this:
<project-list></project-list>
<script>
var project_list = document.getElementsByTagName("project-list")[0]
project_list.custom_method("some_data");
</script>
The custom element is registered in a HTML import like this:
<script>
"use strict";
var currentScript = document._currentScript || document.currentScript;
class ProjectList extends HTMLElement {
createdCallback(){
console.log("created");
}
custom_method(data) {
console.log("custom_method() OK");
console.log(data);
this.innerHTML = data;
}
}
document.registerElement("project-list", ProjectList);
</script>
My question is simple: how to make sure the script in the main html file is called only after the custom element gains its custom_method method?
I'm looking for an elegant solution. Something that the spec authors would have thought of. I don't mind changing the architecture quite a bit (for example by moving the javascript from the main file into another custom element if that is necessary).
Sync HTML Import
As suggested by @dandavis, because of the sync default behaviour of the <link> and <script> elements, you just have to put your tags in the right order: registration before method call.
Or instead you can call your custom method when the DOMContentLoaded or the window.onload event is fired, as below:
window.onload = function()
{
var project_list = document.getElementsByTagName("project-list")[0]
project_list.custom_method("some_data")
}<project-list></project-list>
<script>
"use strict";
var currentScript = document._currentScript || document.currentScript;
class ProjectList extends HTMLElement {
createdCallback(){
console.log("created");
}
custom_method(data) {
console.log("custom_method() OK");
console.log(data);
this.innerHTML = data;
}
}
document.registerElement("project-list", ProjectList);
</script>Async HTML Import
If for some reasons you want to load your HTML Import file asynchronousely, you can wait for the link.onload event. At this time the |<script> inside the import has been already exectued, the custom element registered and created.
<html>
<head>
<title></title>
<meta charset="utf-8" />
<link rel="import" href="projectList.html" id="projectList" async>
<script>
projectList.onload = function ()
{
console.log( "import {loaded}" )
var project_list = document.getElementsByTagName( "project-list" )[0]
project_list.custom_method("some_data")
}
</script>
</head>
<body>
<project-list id="pl"></project-list>
<script>
console.warn( "custom_method is " + pl.custom_method ) //undefined
</script>
</body>
</html>
With WebComponents.js polyfill
In this situation the polyfill won't instantiate the created object immediately after the import is loaded. Instead you should listen to the WebComponentsReady event:
document.addEventListener( "WebComponentsReady", function ()
{
console.log( "WebComponentsReady" )
var project_list = document.getElementsByTagName( "project-list" )[0]
project_list.custom_method( "some_data" )
} )
It works with Firefox, IE 11, and also with Chrome.