Common runtime for the custom szn-* elements.

Usage no npm install needed!

<script type="module">
  import seznamSznElements from 'https://cdn.skypack.dev/@seznam/szn-elements';



This package contains the common runtime for the custom szn-* elements.

Example usage

Note: remove the async attributes and add this markup to the <head> element to prevent the flash of unstyled content:

Simple usage

This section describes the most easy-to-setup usage, which, unfortunately, usually has the worst performance in most browsers.

The recommended use is described in the Advanced usage section.

<script src="/bath/to/babel-polyfill.js"></script>
<script src="/path/to/szn-elements.es3.js"></script>
<script src="/path/to/szn-elements-mutation-observer.es3.js"></script>
<script src="/path/to/custom/szn/element1.js"></script>
<script src="/path/to/custom/szn/element2.js"></script>
<script src="/path/to/custom/szn/element3.js"></script>

This approach allows for bundling all these JS files together... a better approach would be to use HTTP2.

Advanced usage

for (const _ of []);
var forConstSupported = true; // Firefox 52 (ESR), Palemoon and others
    var basePath = '/path/to/szn-elements/';
    var es6 = !!window.Proxy && forConstSupported;
    var browserRuntime;
    if (window.customElements) {
      browserRuntime = 'custom-elements';
    } else {
      browserRuntime = 'mutation-observer.es' + (es6 ? '6' : '3');
        '<script src="' + basePath + 'szn-elements.es' + (es6 ? '6' : '3') +
        '.min.js" async><\/script>' +
        '<script src="' + basePath + browserRuntime + '.min.js" async><\/script>'
<script src="/path/to/custom/szn/element1.js" async></script>
<script src="/path/to/custom/szn/element2.js" async></script>
<script src="/path/to/custom/szn/element3.js" async></script>
<!-- any other SZN elements -->

The script injects two other scripts:

  • the core runtime (szn-elements.es6.min.js or szn-elements.es3.min.js)
  • the browser-specific runtime helper (szn-elements-custom-elements.min.js, szn-elements-mutation-observer.es6.min.js or szn-elements-mutation-observer.es3.min.js).

The script chooses which runtime scripts to inject by detecting the features supported in the current browser, using the more modern features when possible in order to achieve better performance.

Minified version

In case you want to save every byte you can:

<script>for(const _ of[]);var _=true;</script>
}('/path/to/szn-elements/',(self.Proxy&&self._)?6:3,'<script src="','.min.js" async><\/script>')

IE and Edge support

Both IE and Edge (last checked with the 16 version) have no support for the template element and incomplete implementation of the document fragment (no support for firstElementChild). Use a polyfill for these features to enable support in these browsers.

Legacy browser support

To support legacy browsers (IE11, old Androids, etc.), you will need to include a polyfill for the ES2017 features (e.g. the babel-polyfill) before the script above:

<!-- babel polyfill must be inject synchronously -->
<script src="/bath/to/babel-polyfill.js"></script>

To support IE 9-10 is theoretically possible with correct polyfills, use this MutationObserver polyfill (https://www.npmjs.com/package/mutation-observer) like this (IE 10 does not support conditional comments, so we have to use a script):

  if (!window.MutationObserver) {
    document.write('<script src="/path/to/mutationobserver/polyfill.js"></' + 'script>')
<!-- SZN elements code goes here -->

If you need IE8 support as well, use the ES3-compatible polyfill (https://www.npmjs.com/package/mutationobserver-shim) and the following pattern:

<!--[if IE 8]>
<script src="/path/to/mutationobserver/shim.js"></script>
<![if (gt IE 8)|(!IE)]>
<!-- IE 9-10 polyfill code goes here -->
<!-- SZN elements code goes here -->

Alternatively, you may just always include the necessary polyfills, but most of your visitors will have download javascript that they wont even use.