Comparing to null - !== vs != in JavaScript

It is even more simple

var x = null;
    if (x) 6 
    if (!x) 7

the result is

undefined
7

The only value that doesn't equal itself in JavaScript is NaN. If null === null is false, then your JavaScript engine has serious problems ;)

To make sure your conditional statement is well written, always use the braces.

var x = null;
if (x !== null) {
    console.log('x is not equal to null');
}

Your global.User is undefined, not null. When using == they evaluate to equal, but with === the items you are comparing need to be the same type. undefined has the type undefined and null has the type object.

undefined and null are very similar, but they generally mean two very different things. Usually undefined is the result when something has had no value assigned to it, whereas null has a value, and the value is explicitly set to "nothing".