YDK JS - Scope and Closure

gistfile1.txt

Program state: the ability of a language to store value in a variable and later retrive or modify those values. In fact,
the ability store values and pull values out of variables is what gives a program state.

where do those variables live?
where are they store?
how does our program find them?

The set of rules for storing varibales in some location, and for finding those variables at a later time is called scope. 

In traditional compiled-language, a chunk of source code, your program , will undergo typically three steps before it is executed, roughly called "compilcation".

- Tokenizing/lexing (divide program into smaller sets e.g var, a , = , 2, ; etc..)
- parsing ( conver smaller sets into treelike structure also known as abstract sytanx three)
- code-genereation ( converting AST to executable code)

Compiler - Compilation 
Engine - Execution

function foo(a) {
var b = a;
return a + b;
}
var c = foo( 2 );

LHS lookups -> c, a, b
RHS lookups -> foo(2.. , = a, a.. and b ..


ReferenceError -  is scope resolution-failure related, 
whereas - TypeError implies that scope resolution was successful, but that there was an illegal/impossible action attempted against the result.


LEXICAL SCOPE
There are two types of scops 
1) Lexical scope - used by most of the programming languages
2) Dynamic scope - mostly used by scipting languages ( e.g perl, bash)

The first traditional phase of a standard language is called lexing (aka tokenizing).

Lexical scope is based onb where variables and blocks of scope are authored, by you, at write time, and thus is (mostly) set in stone by the time the lexer processes your code

CHAPTER 3 
Function Versus Block Scope

CH 4
function declarations are hoisted but function expressions are not hoisted;