verificação javascript para null variáveis
var myVar=null;
if(myVar === null){
//I am null;
}
if (typeof myVar === 'undefined'){
//myVar is undefined
}
null check-in javascript
if(!pass || !cpass || !email || !cemail || !user) {
// Code here
}
// Which will check for empty strings (""), null, undefined, false and the numbers 0 and NaN