使用jQuery将“ selected”属性添加到下拉选项中

Question

How do I add the attribute "selected" to a drop down menu option based on that option matching some variable?

Here is how the dropdown is populated...

loginOptions = ["First", "Second", "Third"];
        var Login = $( '#Login' );

        for ( var i = 0; i < loginOptions.length; i++ ) {
            Login.append('<option value="'+ loginOptions[i] +'">'+             loginOptions[i] +'</option>');
        }

I want to mark one option as "selected" based on whether or not its value matches another variable. so if loginOption[i] is equal to var existingLoginValue then set that option to 'selected'

Something that would do

if(loginOptions[i] === existingLoginValue){ print 'selected'; };

Thanks!

Answer 1

I'd use .val() at the end of your method, this sets based on value, like this:

$('#Login').val(existingLoginValue);

Similarly, to get the value, call it without any parameters like this:

var currentValue = $('#Login').val();

Answer 2

If you only want to do one value then yeah, the val() works. Otherwise, you can also do this:

$option=$('<option value="'+ loginOptions[i] +'">'+ loginOptions[i]+'</option>').appendTo(Login);
if (loginOptions[i] == existingLoginValue) {
    $option.attr('selected',true)    
}

er, someone pointed out this doesn't really make sense since that would imply multiple options with the same value. I meant to write something like this:

existingLoginValues = ['foo','bar']
$option=$('<option value="'+ loginOptions[i] +'">'+ loginOptions[i]+'</option>').appendTo(Login);
if (existingLoginValues.indexOf(loginOptions[i]) != -1) {
    $option.attr('selected',true)    
}

the indexOf function is supported in most browsers except (of course) IE6. See "Best way to find an item in a JavaScript Array?"

Answer 3

采用

$('#Login').selectedIndex = i