javascript variable is undefined code example

Example 1: javascript typeof undfined

var x;
if (typeof x === 'undefined') {
   // these statements execute
}

Example 2: javascript check if null

if (variable === null) { //Executes only if variable is null but not undefined
  //Code here
}

if (variable == null) { //Executes if variable is null OR undefined
  //Code here
}