7kyu-headTailInitLast.js

// Haskell has some useful functions for dealing with lists:

// $ ghci
// GHCi, version 7.6.3: http://www.haskell.org/ghc/  :? for help
// λ head [1,2,3,4,5]
// 1
// λ tail [1,2,3,4,5]
// [2,3,4,5]
// λ init [1,2,3,4,5]
// [1,2,3,4]
// λ last [1,2,3,4,5]
// 5
// Your job is to implement these functions in your given language. Make sure it doesn't edit the array; that would cause problems! Here's a cheat sheet:

// | HEAD | <----------- TAIL ------------> |
// [  1,  2,  3,  4,  5,  6,  7,  8,  9,  10]
// | <----------- INIT ------------> | LAST |

// head [x] = x
// tail [x] = []
// init [x] = []
// last [x] = x
// Here's how I expect the functions to be called in your language:

// head([1,2,3,4,5]); => 1
// tail([1,2,3,4,5]); => [2,3,4,5]
// Most tests consist of 100 randomly generated arrays, each with four tests, one for each operation. There are 400 tests overall. No empty arrays will be given. Haskell has QuickCheck tests

// P: This program accepts one input, an array, consisting of at least one integer. There will be no empty arrays
// R: This program should return the result of 4 functions performed on the input array, matching the outputs of the head, tail, init, and last array methods as shown in the Haskell example given in the prompt
// E: [1,2,3,4,5] => head => 1, tail => [2,3,4,5], init => [1,2,3,4], last => 5
// P: create four functions, one for each head, tail, init, and last, each of which take an array as an input
//    for head, return the first element of the array (array[0])
//    for tail, return a copy of the array with the first element removed (array.slice(1))
//    for init, return a copy of the array with the last element removed (array.slice(0, -1))
//    for last, return the last element of the array (array[array.length-1])

const head = arr => arr[0];

const tail = arr => arr.slice(1);

const init = arr => arr.slice(0, -1);

const last = arr => arr[arr.length-1];