scope craziness

gistfile1.txt

//  ON the behaviour of 'var'less variable declaration

// if you do this:

function foo(){

   age = 99

}

foo()
console.log(age)
// age => 99, because, if age does not yet exist in the global scope, a 'varless' age inside foo implies it into existence


//-------------RESET----------------//
// if you do this:

function foo(){

    var age = 99

}

foo()
console.log(age)
// age => reference error, because there is no such var as age in the global scope


//-------------RESET----------------//
//  ON the behaviour of variable hoisting

console.log(age)
// age => ReferenceError, it's not defined in the global scope

//-------------RESET----------------//
var age
console.log(age)
// age => undefined, it's been declared, but nothing's been assigned to it, so it's automatically assigned undefined


//-------------RESET----------------//
console.log(age)
// age => undefined, because of some weird behaviour.  When you define a variable (i.e. var age = 99, below), it happens in two parts.  First, JS hoists (hence the term) the declaration to the top of the scope (i.e. above console.log(age), just after the reset) and assigns undefined to it.  When it gets to the line var age = 99, it assigns 99 to it.

var age = 99


console.log(age)
// age => 99, because it's been defined now