In this example, we use JavaScript to loop through all the checkboxes and find which are selected. Note: for in loop is better used for associative arrays, but we'll make it work here too
<script>
function getChecked(){
var selections = new Array();
var x;
var checkBoxes = document.getElementsByName("trees");
for(x in checkBoxes){
if(checkBoxes[x].checked){
selections.push(checkBoxes[x].value);
}
}
//output the checked values
var el = document.getElementById("demo");
el.innerHTML = selections.toString();
}
</script>