@seznam/szn-select-react

v1.4.2

Published

3 years ago

Szn-select integration for React projects.

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jurca

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a11y select web component components szn seznam seznam.cz

szn-select-react

Accessible HTML <select> element replacement with customizable UI. This package provides integration of the szn-select project for React projects.

Usage

First install the package:

npm install --save @seznam/szn-select-react

The <szn-select> (as the SznSelect component) element can be then used the same way as you would use a <select> element in your project. The following example shows various usage options:

import React from 'react'
import SznSelect from '@seznam/szn-select-react'

export default props =>
  <form action='/submit-form' method='post'>
    <div className='inline-form'>
      <label htmlFor='mySelect'>
        Choose one
      </label>
      {/* use the <SznSelect> component as if it was an ordinary <select> element */}
      <SznSelect name='singleOption' id='mySelect' onChange={props.onFirstChanged} defaultValue='2'>
        <option value='1'>first</option>
        <option value='2'>second</option>
        <optgroup label='this is a group'>
          <option value='3'>option groups are supported as well</option>
        </optgroup>
      </SznSelect>
    </div>
    <div className='inline-form'>
      <label htmlFor='anotherSelect'>
        Choose any
      </label>
      <SznSelect name='manyOptions' id='anotherSelect' multiple>
        <option value='foo'>foo</option>
        <option value='foo' title='multiple options may have the same value'>foo 2</option>
        <option value='bar' selected>bar</option>
        <option value='baz' disabled>baz</option>
      </SznSelect>
    </div>
  </form>

Fallback CSS for legacy browsers and no-js scenarios

In order to improve the UX in case of extremely-slowly-loaded JS, legacy browsers or situations where JS is disabled or fails, it is recommended to include the following CSS file in your page to provide fallback styles for the native <select> element that would be where the <SznSelect> component is used:

<link rel="stylesheet" href="https://unpkg.com/@seznam/[email protected]/szn-select-nojs.css">

Configuring the loader

The component, by default, injects the szn-select's loader script into the <head> to load the latest compatible version of szn-select using the latest compatible loader. This technique is used automatically provide bugfixes and compatibility updates (compatibility with the assistive technologies does shift in time, unfortunately).

Another thing the loader does for you is selecting the smallest, best-performing bundle for the current browser. This means that the modern browsers (e.g. Chrome) tend to download smaller bundles than the legacy browsers (e.g. Internet Explorer).

The downside of this is that the browser has to download two more JS files from the unpkg.com's CDN (by default, configurable) to enable all features of the <SznSelect> component.

This behavior may be, if needed, modified using the loader options passed as an object to the component in the loaderOptions prop:

<SznSelect loaderOptions={{ /* loader options go here, see below for details */ }}>
  select's option elements go here
</SznSelect>

Note that only the first <SznSelect> instance activated by React will perform the loading, therefore passing different options to multiple SznSelects on a single page might result in inconsistent or unexpected results. To avoid this, a common pattern used is using a higher-order component, as seen below:

import React from 'react'
import SznSelect from '@seznam/szn-select-react'

const LOADER_OPTIONS = {
  // loaders options go here, see below for details
}

export default props =>
  // Make sure you specify the loaderOptions props as last so that loader
  // options that were passed-in accidentally will be overridden by your
  // intended configuration
  <SznSelect {...props} loaderOptions={LOADER_OPTIONS}>
    {props.children}
  </SznSelect>

The loader options are:

enable - whether to use a loader at all. This defaults to true, setting this option to false is useful when using a self-hosted deployment (see below). Use this option with care as it usually leads to getting no updates and bugfixes until you update the dependencies in your project manually.
useEmbeddedLoader - When set to true, the component will use a more light-weight loader to load the szn-element's bundle. This saves a single (tiny) JavaScript file download. This usually leads to the same results as using a full-feature loader, however, if there are bugfixes available for the loader, you will might not receive them in certain situations. In most cases it is OK to set this option to true. Defaults to false.
useAsyncLoading - when set to true, the async attribute will be set on the <script> elements used to load the szn-select's JavaScript logic. Since the loader is always triggered after the DOMContentLoaded event, the scripts will be loaded asynchronously anyway regardless of this flag. This option is simply exposed from the underlying loader mechanics. Defaults to true.
urls - an object that provides URL overrides for the loader:
- package - the URL at which the @seznam/szn-select package's files are available. This can be overridden on per-file basis using the options below. Defaults to https://unpkg.com/@seznam/[email protected]/, the trailing slash is optional.
  It is recommended to use a semver version range when using unpkg or a similar JS CDN, such as 1.x to automatically receive the latest compatible version with the most recent bugfixes and compatibility updates.
- loader - the URL override for the full-featured loader. This option has no effect when the useEmbeddedLoader is set to true.
- es3 - the URL override for the ES3-compatible implementation of the szn-select element. This is used on legacy browsers if the implementation for the szn-tethered helper element and the szn-elements runtime is already loaded.
- es2016 - the URL override for the ES2016-compatible implementation of the szn-select element. This is used on modern browsers if the implementation for the szn-tethered helper element and the szn-elements runtime is already loaded.
- bundle-elements.es3 - the URL override for the ES3-compatible implementation of the szn-select and szn-tethered elements. This is used on legacy browsers if the szn-elements runtime is already loaded.
- bundle-elements.es2016 - the URL override for the ES2016-compatible implementation of the szn-select and szn-tethered elements. This is used on modern browsers if the szn-elements runtime is already loaded.
- bundle-full.es3 - the URL override the ES3-compatible implementation of the szn-select and szn-tethered elements and the szn-elements runtime. This is used on legacy browsers if no dependencies are loaded yet.
- bundle-full.es2016 - the URL override the ES2016-compatible implementation of the szn-select and szn-tethered elements and the szn-elements runtime. This is used on modern browsers if no dependencies are loaded yet.
- bundle-full.ce - the URL override the ES2016-compatible implementation of the szn-select and szn-tethered elements and the szn-elements runtime. This is used on modern browsers that support the custom elements API if no dependencies are loaded yet.

Synchronous szn-select element loading

The downside of letting the <SznSelect> element handle all the work is that the implementation of the underlying <szn-select> element is loaded asynchronously. This may lead to a FOUC or seeing the native <select> element with the fallback styles applied for a brief moment.

This can be improved by using synchronous loading of the <szn-select> element by injecting the loader into the page ourselves (notice there is no async nor defer attribute):

<script src="https://unpkg.com/@seznam/[email protected]/loader.min.js"></script>

Since the script would be executed synchronously, the loader will inject the bundle using document.write(), which will load the <szn-select> element before the DOMContentLoaded event occurs. The <SznSelect> component will recognize that the szn-select element has been already loaded and will not inject the loader repeatedly.

The downside to the example above is that the script is loaded from another domain than your website, and Chrome will block the loading the of bundle on 2G connections. This can be resolved by hosting the files yourselves (see below).

There is another issue to be considered when using server-side rendering in combination with React: Executing the <szn-select>'s bundle before the React rehydrates the server-rendered DOM will result in the DOM being different from React's expectations. This will cause only a warning with React 16 and function normally, however, React 15 or older will probably remove the <szn-select>s UI elements, which will result in an invisible unusable select. To fix this, run React's rehydration (ReactDOM.hydrate() in React 16, ReactDOM.render() in React 15 or older) synchronously during document parsing and before the loader script is included, and setting the enable flag in the loader options to false.

Self-hosted deployment

For some reason or another it might be practical for you to host the bundle files yourselves. First, start by installing the szn-select package:

npm install --save @seznam/[email protected]

Next, make the files in the npm module available in your project over HTTP as static assets.

The final step depends on your preferred way of loading the bundle:

if you leave the bundle loading to the <SznSelect> component, provide the loaderOptions prop with the urls object. Having the urls.package option is usually enough, point it to your local URL at which you made the szn-select's files available.
if you are using synchronous loading (see above), use these data attributes on the loader's <script> element.

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