Based on the polyfill for HTMLImports https://github.com/webcomponents/html-imports.
The polyfill hosts the included documents in the include link element. E.g.
<link rel="include" href="my-element.html">
<!-- becomes -->
<link rel="include" href="my-element.html">
<!-- my-element.html contents -->
</link>The polyfill fires the HTMLIncludesLoaded event when imports are loaded, and exposes the HTMLImports.whenReady method. This api is necessary because unlike the native implementation, script elements do not force imports to resolve. Instead, users should wrap code in either an HTMLIncludesLoaded handler or after load time in an HTMLIncludes.whenReady(callback) call.
The polyfill provides the HTMLIncludes.includeForElement() method which can be used to retrieve the <link rel=include> that included an element.
The polyfill appends the included contents to the <link> itself to leverage the native implementation of Custom Elements, which expects scripts upgrading the CustomElementRegistry to be connected to the main document.
As a consequence, .ownerDocument will be the main document, while .parentNode of the included children will be the <link rel=include> itself. Consider using HTMLIncludes.includeForElement() in these cases. e.g:
const ownerDoc = HTMLIncludes.includeForElement(document.currentScript);
let someElement = ownerDoc.querySelector('some-element');
if (ownerDoc !== HTMLIncludes.includeForElement(someElement)) {
// This element is contained in another import, skip.
someElement = null;
}If you require document isolation, use html-imports#v0.
The polyfill supports dynamically added imports by observing mutations in <head> and within other imports; it won't detect imports appended in <body>.
If you require to append includes in <body>, notify the polyfill of these additions using the method HTMLIncludes.loadIncludes(document.body).
In IE/Edge, appending <link rel=stylesheet> in a node that is not <head> breaks the cascading order; the polyfill checks if an import contains a <link rel=stylesheet>, and moves all the imported <link rel=stylesheet> and <style> to <head>. It drops a placeholder element in their original place and assigns a reference to the applied element, placeholder.__appliedElement. e.g.
my-element.html imports a stylesheet and applies a style:
<link rel="stylesheet" href="my-linked-style.css">
<style> .blue { color: blue }; </style>And is imported in index.html:
<head>
<link rel="import" href="my-element.html">
</head>This is how the resolved import will look like:
<head>
<link rel="stylesheet" href="my-linked-style.css">
<style> .blue { color: blue }; </style>
<link rel="include" href="my-element.html">
<link type="include-placeholder">
<style type="include-placeholder"></style>
</link>
</head>The placeholders contain a reference to the applied element:
var myInclude = document.head.querySelector('link[rel=include]').include;
var link = myInclude.querySelector('link');
console.log(link.__appliedElement || link);
var style = myInclude.querySelector('style');
console.log(style.__appliedElement || style);$ git clone https://github.com/AaronNGray/html-includes.git
$ cd html-includes
$ npm i
$ bower i
$ gulp$ npm i -g web-component-tester
$ wct