Make textareas able to insert tabs

tabable.js

function tab(event, obj) {
    var tabKeyCode = 9;
    if (event.which) // mozilla
    var keycode = event.which;
    else // ie
    var keycode = event.keyCode;
    if (keycode == tabKeyCode) {
        if (event.type == "keydown") {
            if (obj.setSelectionRange) {
                // mozilla
                var s = obj.selectionStart;
                var e = obj.selectionEnd;
                obj.value = obj.value.substring(0, s) +
                    "\t" + obj.value.substr(e);
                obj.setSelectionRange(s + 1, s + 1);
                obj.focus();
            } else if (obj.createTextRange) {
                // ie
                document.selection.createRange().text = "\t"
                obj.onblur = function () {
                    this.focus();
                    this.onblur = null;
                };
            } else {
                // unsupported browsers
            }
        }
        if (event.returnValue) // ie ?
        event.returnValue = false;
        if (event.preventDefault) // dom
        event.preventDefault();
        return false; // should work in all browsers
    }
    return true;
}