Classic javascript doing javascript things (this is why they introduced let and const)

Kind of. With hoisting, the compiler/interpreter will find variable declarations and execute them before executing the rest of the code. Hoisting leaves the variables as undefined until the code assigning the value to the variable is executed. Hoisting does not initialize the variables.

For example:

console.log(foo);
var foo;
//Expected output: console logs 'null'

foo = 'bar';
console.log(foo);
var foo;
//Expected output: console logs 'bar'

console.log(foo === undefined);
var foo;
//Expected output: console logs 'true'

This means you can essentially write your code with variable declarations at the end, but it will still be executed as though the declarations were at the beginning. Your initializations and value assignments will still be executed as normal.

This is a feature that you should probably avoid because I honestly cannot think of any good use case for it that won't end up causing confusion, but it is important to understand that every variable within your scope will be declared at the beginning of execution regardless of where it is written within your code.

var a;
(function() {
  a='hoisted';
  console.log(a);
  var a;
})()
console.log(a);

Should log hoisted and then undefined, showing that you've assigned to the later-declared var a which was hoisted vs the external global a.

It's not a gender tho... Or is it?
vsauce music starts playing

Good point!

There are two kinds of "null" that are often called out as mistakes, you may be thinking of. One is the null reference, as found in languages like C and Java, which Tony Hoare, who created it for ALGOL back in the sixties, has called his "billion dollar mistake". The other is the three-valued-logic of null in SQL, which is almost as bad.

There's nothing wrong with "null", necessarily, in other contexts, although I do think a more clear name for whatever it means in any given context might be better.

I can't comment anything without the internet. Checkmate atheist.