1if (variable !== null) {
2  console.log("Var is NOT null");
3}

1if (variable == null) {
2    // variable is either null or undefined
3}

1if (variable === null) { //Executes only if variable is null but not undefined
2  //Code here
3}
4
5if (variable == null) { //Executes if variable is null OR undefined
6  //Code here
7}

1var myVar=null;
2
3if(myVar === null){
4    //I am null;
5}
6
7if (typeof myVar === 'undefined'){
8    //myVar is undefined
9}
10

1if(!pass || !cpass || !email || !cemail || !user) {
2   // Code here
3}
4// Which will check for empty strings (""), null, undefined, false and the numbers 0 and NaN