simplete

Simplete /sɪmˈpliːt/

Simplete (demo) is a custom element for autocompletion, using HTML fragments dynamically requested from the server. It is suitable both for context completion and quicksearch results.

Simplete relies on established form semantics and leaves markup up to the server. In contrast to most autocompletion libraries (see alternatives), which typically rely on JSON responses and client-side templating, this typically reduces complexity and increases flexibility.

In addition to progressive enhancement, accessibility has been a major driver in the design and implementation (largely thanks to Heydon Pickering's inspiring evangelism).

Usage

We start out with a fairly straightforward form:

<form action="/search" method="get">
    <simplete-form>
        <label>
            search
            <input type="search" name="query">
        </label>
    </simplete-form>

    <button>search</button>
</form>

Or, if we want to target different resources:

<form action="/search" method="get">
    <simplete-form action="/search/suggestions" method="get">
        <label>
            search
            <input type="search" name="query">
        </label>
    </simplete-form>

    <button>search</button>
</form>

Typing into that search field will result in a form submission (i.e. a GET /search/suggestions?query=… AJAX request).

Typically the server would respond with HTML like the following:

<ol aria-label="2 search suggestions">
    <li>
        <input type="hidden" value="foo">
        lorem ipsum
    </li>
    <li>
        <input type="hidden" value="bar">
        dolor sit amet
    </li>
</ol>

Selecting an item from that list will populate the search field with the corresponding value or the text content of the item, which may subsequently be used to submit the surrounding form. (Note that keyboard-based submission of the surrounding form is only suppressed while navigating results.)

The server might also choose to respond with immediate results rather than query suggestions:

<ol aria-label="2 search suggestions">
    <li>
        <a href="http://example.org">example.org</a>
    </li>
    <li>
        <a href="http://example.com">example.com</a>
    </li>
</ol>

In fact, such HTML responses are not limited to any particular markup: The server is free to include multiple lists, contextual feedback messages or whatever seems appropriate (see customization below).

The styles directory contains some basic suggested CSS while demo/demo.css contains a rudimentary theme.

Note that when a result is selected, a "simplete-selection" custom event is triggered on the associated <simplete-form> element. The respective value is accessible via event.detail.value.

Customization

<simplete-form> may optionally be configured with the following attributes:

• search-field-selector (defaults to "input[type=search]") is a selector identifying a search field (must be a unique child element)
• query-delay (defaults to 200) is the number of milliseconds to wait before triggering an HTTP request
• min-length (defaults to 1) is the minimal input length required before triggering an HTTP request
• cors is a boolean attribute which, if present, ensures credentials are included with cross-origin requests

<simplete-form search-field-selector="textarea" query-delay="100" cors>
    <textarea></textarea>

    <label>
        <input type="checkbox" name="case-sensitive" value="1">
        case-sensitive
    </label>
</simplete-form>

Similarly, server responses may optionally use attributes specify how the response should be interpreted:

• data-autocomplete-status will be announced to assistive technologies
• data-item-selector (defaults to "li") identifies results
• data-field-selector (defaults to "input[type=hidden]") identifies fields whose value will be used for populating the search field
• data-result-selector (defaults to "a") identifies elements which represent immediate results

<section data-autocomplete-status="2 search suggestions available"
        data-item-selector="article h3"
        data-field-selector="button[type=button]"
        data-result-selector="button[type=submit]">
    <article>
        <h3>Hello World</h3>
        <p>lorem ipsum dolor sit amet</p>
        <button type="submit">upvote</button>
    </article>

    <article>
        <h3>…</h3>
        <p>…</p>
        <button type="submit">upvote</button>
    </article>
</simplete-form>

Accessibility

Simplete will add the ARIA roles and attributes necessary in order for the autocomplete component to work with assistive technologies.

While it is possible to customize the component with arbitrary HTML, we recommend using a semantic HTML list (ol or ul) with a corresponding aria-label, because we have performed screenreader tests for this markup (aria-label was necessary in order for the list of suggestions to be announced as a list in NVDA).

We also recommend performing usability testing for your implementation of the component. The general expectation for a component like this is that selecting a result from the list of suggestions will behave in the same way as if that suggestion were entered into the search field and the form were submitted. If your links do not behave accordingly (e.g. if your search suggestions are links to a concrete page instead of to a list of search suggestions), you will need to find a way to communicate this to the user.

Dependencies

Simplete has no external dependencies (though it includes a few tiny utility functions from uitil).

However, it does rely on modern browser features which might have to be polyfilled:

• custom elements — suggested polyfill: @ungap/custom-elements
• fetch — suggested polyfill: whatwg-fetch or unfetch
• CustomEvent
• Element#closest
• Array#from
• Object.assign

The Financial Times's excellent polyfill service is a good source for additional polyfills.

The source code is written in ES2015, without relying on non-standardized language extensions.

Contributing

• ensure Node is installed
• npm install downloads dependencies
• npm start launches a persistent process to automatically update the development bundle
• npm run compile creates the distribution bundle
• npm test executes the test suite

Alternatives

• Awesomplete
• typeahead.js
• jQuery UI Autocomplete
• …