hoisting

hoisting

https://github.com/getify/You-Dont-Know-JS/blob/master/scope%20&%20closures/ch4.md

"When you see var a = 2;, you probably think of that as one statement. 
But JavaScript actually thinks of it as two statements: var a; and a = 2;.
The first statement, the declaration, is processed during the compilation phase.
The second statement, the assignment, is left in place for the execution phase."

- declaration comes before the assignment
- function declarations are hoisted, but function expression are not

ex. 
    foo(); // TypeError
    bar(); // ReferenceError
    
    var foo = function bar() {
        ...
    };
    
    1. foo // TypeError: undefined is not a function
        because var 'foo' is declared, and by default it is assigned to 'undefined'. It has not been assigned to be a function yet
    2. bar //ReferenceError: bar is not defined
        because the statement var foo = function bar() declares a variable 'foo',
        but the assignment of function bar() {...} has not yet been executed, therefore, function bar() is
        undefined