filter.js

// creating a new function without members that fail a truth step
var arr = [0, 1, 2, 3]

// imperative
var arrIm  = [],
    isEven = function(a){ return a % 2 === 0 }

for ( var i = 0; i < arr.length; i += 1 ) {
  if ( isEven(arr[i]) ) arrIm.push(arr[i])
}

// functional
var arrFp = arr.filter(isEven)

map.js

// creating a new function with new values.
var arr = [0, 1, 2, 3]

// imperative
var arrIm = []

for ( var i = 0; i < arr.length; i += 1 ) {
  arrIm.push(arr[i] + 1)
}

// functional
var inc   = function(a){ return a + 1 },
    arrFp = arr.map(inc)