The basics

Include an import on your page by declaring a

<link rel="import">

like this:

The URL of an import is called an import location. To load content from another domain, the import location needs to be CORS-enabled:

<!-- Resources on other origins must be CORS-enabled. -->
<link rel="import" href="http://example.com/elements.html">

Feature detection and support

To detect support, check if.import exists on the element:

function supportsImports() {
  return 'import' in document.createElement('link');
}

if (supportsImports()) {
  // Good to go!
} else {
  // Use other libraries/require systems to load files.
}