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var people = ['Jim', 'Bob', 'Jane', 'Jill'];
var welcomes = people.map(function(name) {
  return 'Hi' + ' ' + name + '!';
});

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JavaScript is a protypal language but has syntax that is more similar to a classical language which can be confusing.

Function as module (using self-executing function ) is a way to do functions better in some instances.
Function as module safeguards against values being exposed b/c it limits scope:
(function () {
  var ...
  function ...
  function ...
}());

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hoisting in functions concern variables

The var statement gets spit into two parts:
  The declaration part gets hoisted to the top of the function, initializing with undefined.
  The initialization part turns into an ordinary assignment.
  
    var myVar = 0, myOtherVar;
    
  Expands into
    

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function expression
function
optional name
parameters
  wrapped in ()
  zero or more names
  separated by a comma
body
  wrapped in {}
  zero or more statements

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expression
if
switch
while
do
for
break
continue
return
try/throw

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number.toString(radix);
number can be a variable

radix - optional and determines the base to use for representing a numeric value. Must be an integer between 2 and 36.
2 - binary
8 - octal
16 - hexadecimal- often used with hex values used in styling such as when changing color, background-color etc. 

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Closure is a central idea in JavaScript.

The context of an inner function includes the sclope of the outer function.
An inner function enjoys that context even after the parent functions have returned.

function scope works like block scope.

Global:
var names = ['zero', 'one', 'two',
    'three', 'four', 'five', 'six',

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(function () {
  return expression:
}())

works except if any of the following are used in function
var
function
break
continue
return

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Recursion - when a function calls itself.
Discovered with LISP around 1958.

A great example of recursion is the quicksort
algorithm:
  1. use quicksort to divide the array into two groups, low and high
     if alpha, put all items that begin with a-m into 1st group and the remaining in 2nd group
     if numbers, determine the mid-point and put lower nums in 1st group and the remaining in 2nd group unless this type of dividing would          result in one group being much larger than the other, if so, adj mid-point
  2. call quicksort again on each group containing more than one element.

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Where did functions come from?
subroutines

In earlier languages, subroutines were written and used in various ways.  
Subroutines were called and could return something.
They were also referred to as: sub, procedure, proc, func, functions, lambda and are all the same idea.

What advantages do subroutines give us?
code reuse which was originally a memory conserving device
decomposition - take a complicated problem and break it down into subroutines