function checkAll(name) {
var el = document.getElementsByTagName('input');
var len = el.length;
for(var i=0; i<len; i++){
if((el[i].type=="checkbox") && (el[i].name==name)){
el[i].checked = true;
}
}
}
function clearAll(name) {
var el = document.getElementsByTagName('input');
var len = el.length;
for(var i=0; i<len; i++){
if((el[i].type=="checkbox") && (el[i].name==name)){
el[i].checked = false;
}
}

}

全選<input type="checkbox" id="qx" onClick="if(this.checked==true) { checkAll('productId'); } else { clearAll('productId'); }" id="qx"/>