HTML <select>: focus option based on user in

问题:

I have an HTML select element:

<select id='poetslist'>
    <option value="shakespeare">William Shakespeare</option>
    <option value="milton">John Milton</option>
    <option value="keats">John Keats</option>
    <option value="wordsworth">William Wordsworth</option>
    <option value="larkin">Phillip Larkin</option>
</select>

In Chrome, when the page loads, the William Shakespeare option is selected. If the user starts typing 'Phil', the list focusses itself on Phillip Larkin. Familiar behaviour.

What I'd like to do (preferably using jQuery) is also allow the user to type the initials of the poet and have the relevant option come into focus.

So if you typed JK, then the John Keats option should come into focus. JM and John Milton, etc.

I don't even know how the HTML select element works, whether it's different in different browsers, etc - and it seems to be hard to find good documentation for this.

Can anyone figure out a smart way to do this in jQuery?

回答1:

Here is a complete solution:

1. Add attributes to each option, as @JMC suggests. However, I'd prepend the attribute name with "data-" to be in line with HTML5 standards. jQuery (as of v1.4.3) also supports retrieving attributes beginning with "data-" using .data().
2. Bind to the keypress event. This is more correct than keyup for the following reasons:
   1. Semantically, keypress means user input has happened, while keyup means the physical key is lifted. For example, holding down a key will generated multiple keypress events (for each character that appears on screen), while only one keyup event. Keypress is also not prone to incorrectly receiving the order of keypresses when the user types "QW" quickly, but lifts the "W" key (a keyup) before the "Q" key.
   2. Keyup will be generated on non-character keys such as the arrows, backspace, etc..., while keypress will not.
3. Use a timer to distinguish between two isolated key presses and a single sequence of key presses, e.g. did the user mean "W" for William Shakespeare and then "P" for Phillip Larkin, or just "WP" for ... Whatever Poet.

HTML

<select id="poetslist">
    <option value="shakespeare" data-initial="WS">William Shakespeare</option>
    <option value="milton" data-initial="JM">John Milton</option>
    <option value="keats" data-initial="JK">John Keats</option>
    <option value="wordsworth" data-initial="WW">William Wordsworth</option>
    <option value="larkin" data-initial="PL">Phillip Larkin</option>
</select>

Javascript

var timer = null, initials = "";

$("#poetslist").keypress(function (e) {
    initials += String.fromCharCode(e.which).toUpperCase();

    // Look for option with initials beginning with the typed chars
    $(this).find("option").filter(function () {
        return $(this).data("initial").toUpperCase().indexOf(initials) === 0;
    }).first().attr("selected", true);

    // Set/reset timer
    if (timer) {
        clearTimeout(timer);
        timer = null;
    }
    timer = setTimeout(function () {
        timer = null;
        initials = "";
    }, 2000); // Max 2 second pause allowed between key presses

    return false;
});

回答2:

With @Charlie's answer in mind, if you have access to build the html in the first place, it might be easiest to add an extra attribute to the option element, like

<option init="WW" value="wordsworth">William Wordsworth</option>
<option init="PL" value="larkin">Phillip Larkin</opt

If you can't do this on the server-end, jQuery could easily insert an extra attribute to an option based on it's value. Assuming, of course, that you know in advance each of the values you'll have in there.

After getting the extra attribute into the option, it would just be a matter of checking those values on keyup of the search box.

回答3:

The basic magic you need is to set the property "selected" on one of the options. Give each one an ID. Then use

$('#anId').attr('selected','selected');

See also this SO question.

Now, for the selection behavior, you probably need to intercept the key pressed events and do your own logic. The trickiest part is probably figuring out what to do for odd cases, like what happens when someone type "JKM" -- Keats or Milton?