<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd"><html> <head> <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"> <title>Untitled Document</title> <script type="text/javascript"> var selected = []; function doSomething() { var last_index = getLastIndex(); alert('Last selected option index: '+last_index); alert('Selected array: '+selected.toSource()); } function getLastIndex() { var el = document.getElementById('x'); // Loop select options for(i=0;i<el.length;i++) { // Look in selected array for this option index selected_index = selected.indexOf(i,0,true); // Exists in selected if(selected_index > -1) { // Not selected, remove if(el.options[i].selected == false) { selected.splice(selected_index, 1); } // Doesn't exist in selected, append } else if(el.options[i].selected && selected_index == -1) { selected.push(i); return i; } } // If one was removed, and at least one is still selected if(selected.length > 0) { return selected[selected.length-1]; } // Nothing is selected, or the one element in selected was just removed return -1; } // Array.indexOf( value, begin, strict ) - Return index of the first element that matches value Array.prototype.indexOf = function(v,b,s) { for(var i = +b || 0, l = this.length; i < l; i++ ) { if( this[i]===v || s && this[i]==v ) { return i; } } // Not found return -1; }; </script> </head> <body> <select id="x" onchange="doSomething();" multiple="multiple" size="5"> <option value="1">One</option> <option value="2">Two</option> <option value="3">Three</option> <option value="4">Four</option> <option value="5">Five</option> </select> </body></html>