Question

$('#sellist option').each(function(index) {
    var str ='4/5/8';
    var substr = str.split('/');
    if (substr[0] == $(this).attr('value')) {
        $(this).attr('selected','selected');
        alert('hi'); ///For check
    }
});

Every thing works fine and alert is fired. I havent any error in console. But #sellist option is not selected which I want. What is my problem. Thanks.

Answer 1

Your code is working fine. It is just selecting the first element of your array, 4 because you are not looping through the array, you just use substr[0] to get the first value.

To see that it works I changed the initial value to 7:

$('#sellist option').each(function(index) {
    var str = "7/5/8";
    var substr = str.split('/');

    if (substr[0] == $(this).val()) {
        $(this).attr('selected', 'selected');
        alert($(this).val()); ///For check
    }
});

Fiddle to show it works

OP Clarified he want to loop around array

To loop through your array and select each value in the multiple select, use this:

$('#sellist option').each(function(index) {
    var str = "4/5/8";
    var substr = str.split('/');

    for (var i = 0; i < substr.length; i++) {
        if (substr[i] == $(this).val()) {
            $(this).attr('selected', 'selected');
        }
    }
});

Update fiddle