How to get selected text with JavaScript

I'm a little confused why doesn't this code work!

The HTML Markup:

<div id="diva"><b>Score</b> some <i>goals</i></div>
<div id="soda"></div>

The JavaScript code:

function GetSelectedText () {
if (window.getSelection) {  // all browsers, except IE before version 9
    var range = window.getSelection ();
    alert (range.toString ());
} 
else {
    if (document.selection.createRange) { // Internet Explorer
        var range = document.selection.createRange ();
        alert (range.text);
    }
}
}

var butn = document.getElementById("soda");
butn.onclick = function(){
    GetSelectedText();
}

One problem that you may well be experiencing is that in some browsers (notably IE), by the time the button's click event fires, the selection has been destroyed. You can fix this by using the mousedown event instead (which still allows the selection to be destroyed, but only after the event has been handled), or by making the button unselectable.

I assume your button is not an actual button input, because this behaviour only happens for regular elements.

Demo: http://jsfiddle.net/L9bvU/1/

function GetSelectedText () {
    if (window.getSelection) {  // all browsers, except IE before version 9
        var range = window.getSelection ();
        alert (range.toString ());
    } 
    else {
        if (document.selection.createRange) { // Internet Explorer
            var range = document.selection.createRange ();
            alert (range.text);
        }
    }
}

span {
    background-color: #ccc;
    padding: 3px;
    border: solid gray 1px;
    
}

*[unselectable="on"] {
   -moz-user-select: -moz-none;
   -khtml-user-select: none;
   -webkit-user-select: none;

   /*
     Introduced in IE 10.
     See http://ie.microsoft.com/testdrive/HTML5/msUserSelect/
   */
   -ms-user-select: none;
   user-select: none;
}

<div contenteditable="true">Please select some of this text and press a button below</div>

<span onclick="GetSelectedText()">Click</span>
<span onmousedown="GetSelectedText()">Mousedown</span>
<span unselectable="on" onclick="GetSelectedText()">Click, unselectable</span>