How to implement all or none using js

 
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; 
} 
} 

} 

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