选中getElementById不能选择多个选项

Question

I have a function in javascript that should allow me to select more than one option, but it only selects the first one.

Javascript:

 function index(){
        var a="${staffindex}".replace("[","");
        var b=a.replace("]","");
        var index1=b.split(",");
        for(var i=0;i<index1.length;i++)
            document.getElementById("Staff")[index1[i]].selected=true;
        }

HTML:

<select multiple="multiple" id="Staff" name=staff>
                <option value = "1" >option1</option>
        <option value = "2" >option2</option>
        <option value = "3" >option3</option>
        <option value = "4" >option4</option>
        <option value = "5" >option5</option>
</select>

index1 is an array of numbers received from a java class.
Thanks for any help!

Answer 1

你忘了使用options数组：

document.getElementById("Staff").options[index1[i]].selected=true;

Answer 2

getElementById() function in javascript selects only one element. Here it only selects the <select> tag since it has the id as Staff and not its options. You can however access its options as

getElementById("Staff").options[option_number];

Answer 3

Try this:

function index(){
    var a="${staffindex}".replace("[","");
    var b=a.replace("]","");
    var index1=b.split(",");
    for(var i=0;i<index1.length;i++)
        document.getElementById("Staff").options[index1[i]].selected=true;
}

That options is very neccessary here!