Javascript函数无法按预期在IE中运行

Question

This code below works fine in chrome, Firefox and Edge. But when I try this same code in html I get the following error.

SCRIPT5009: 'ddlTest' is undefined

<select id="ddlTest">
    <option>1</option>
    <option>2</option>
    <option>3</option>
</select>

<script>

    function testFunc() {
        var y = (ddlTest).value;
        alert(y);
    }

</script>

Is there a way I can get around this in IE , other than doing :

document.getElementById('ddlTest').value

Answer 1

The feature to have a property on window to access an element by ID was added in HTML5.

The HTML5 standard specifies that the window object must have a property key whose value is elem if...

• there is exactly one DOM element elem whose property id has the value key .
• there is exactly one DOM element elem whose property name has the value key . elem ’s tag must be one of: a, applet, area, embed, form, frame, frameset, iframe, img, object.

~ http://2ality.com/2012/08/ids-are-global.html

However, you should not use this in your actual code -- use document.getElementByID('elem') instead:

As a general rule, relying on this will lead to brittle code. Which IDs end up mapping to this API can vary over time, as new features are added to the Web platform, for example. Instead of this, use document.getElementById() or document.querySelector() .

~ https://html.spec.whatwg.org/#named-access-on-the-window-object

Answer 2

No, the only way to do it is to get the element through the document:

function testFunc() {
    var ddlTest = document.getElementById('ddlTest');
    var y = ddlTest && ddlTest.value;
    alert(y);
}