Very weird Chrome behavior in an open (focused) “select” element

问题

Here's a <select> element:

<select>
    <option>Hello</option>
    <option>Banana</option>
    <option>Balloon</option>
    <option>Something</option>
    <option>Potato</option>
    <option>Cleveland</option>
</select>

Here's a little bit of JavaScript (a jQuery "ready" handler):

$(function() {

    function foo() {
        var s = $('select').find(':selected');
    }

    setInterval(foo, 200);
});

Here is the jsfiddle for this question..

The handler sets up an interval timer which, every 200 milliseconds, finds the currently-selected <option> of the <select>, and does nothing at all with it. When I run the fiddle in Chrome (13.0.782.112), and I click on the <select> element, and then try to select an entry, the selection highlight keeps jumping back to the first selected element. I can click on any of the <option> elements shown and that works, of course, and then it does the same thing the next time.

Now, if I change the timer handler so that it doesn't use jQuery to find the currently-selected <option> element, as follows:

$(function() {

    function foo() {
        var select = $('select')[0];
        var s = $(select.options[select.selectedIndex]);
    }

    setInterval(foo, 200);
});

then I no longer see the effect.

Firefox does not do this. I haven't tried Safari yet.

Personally I think that something's doing something wrong here. Is it Chrome? jQuery?

edit — one more detail - I'm running Chrome on Linux. I'll try Windows in a sec. (edit same in Windows.)

回答1:

Change the code to:

function foo() {
    var s = $('select option:selected');
}

setInterval(foo, 200);

Not sure why exactly it does this, but my guess would be that it's related to the way pseudoselectors work in jQuery. They're implemented as functions which are paired with the name of the selector (In this case "selected"). Consequently they are run against every possible element in the context (not just those which could potentially be selected).

Maybe there some sort of weird ghost element against which the "selected" pseudoselector is being executed when it shouldn't. The solution here is that I restrict the context to options before doing the pseudoselector. Always a good thing to do.

来源：https://stackoverflow.com/questions/7183522/very-weird-chrome-behavior-in-an-open-focused-select-element