All Ways to Create Functions.js

/* ES6 the Lazy Way */

var nums = [1, 2, 3, 4, 5, 6]

// You don't have to use braces when it is a simple expression
// No need to say return, it just knows
// The fat arrow is creating the function 
// If we have one arg, no need to add parens 
var odds = nums.map(v => v + 1); // [ 2, 3, 4, 5, 6, 7 ]

// Same things as above is the take away
// We have to use `()` if we have more than one arg
var all = nums.map((v, i) => v + i); // [ 1, 3, 5, 7, 9, 11 ]

// We return an array of objects without saying return explicitly 
// If we include comma we have to add `()` to return
// In this case we have to wrap the object in `()`, same for arrays
var pairs = nums.map(v => ({even: v, odd: v + 1})); 
/*
Output: 
[ { even: 1, odd: 2 },
  { even: 2, odd: 3 },
  { even: 3, odd: 4 },
  { even: 4, odd: 5 },
  { even: 5, odd: 6 },
  { even: 6, odd: 7 } ]
*/

// 
var pairs = nums.map(v => {
  ({even: v, odd: v + 1})
}); // [ undefined, undefined, undefined, undefined, undefined, undefined ]

// Cannot use `()` if you want more than one statement inside the function
// var pairs = nums.map(v => 
//   var temp = 2 + v;
//   ({even: temp, odd: temp + 1})
// );

// NOTE: You have to use `{}`, remove the `()` and add the return keyword
var pairs = nums.map(v => {
  var temp = 2 + v;
  return {even: temp, odd: temp + 1}
});