checked and unchecked all checkbox value

function prepare(form_id) {
var formblock;
formblock= document.getElementById(form_id);
forminputs = formblock.getElementsByTagName('input');
return forminputs;
}

function select_all(formname,name, value) {
forminputs = prepare(formname);
for (i = 0; i < forminputs.length; i++) {
// regex here to check name attribute
var regex = new RegExp(name, "i");
if (regex.test(forminputs[i].getAttribute('name'))) {
if (value == '1') {
forminputs[i].checked = true;
} else {
forminputs[i].checked = false;
}
}
}
}

if (window.addEventListener) {
window.addEventListener("load", prepare, false);
} else if (window.attachEvent) {
window.attachEvent("onload", prepare)
} else if (document.getElementById) {
window.onload = prepare;
}