mutation.js

/*
Return true if the string in the first element of the array contains all of the letters of the string in the second element of the array.

mutation(["hello", "hey"])                    // false.
mutation(["hello", "Hello"])                  // true.
mutation(["zyxwvutsrqponmlkjihgfedcba", "qrstu"])       // true.
mutation(["Mary", "Army"])                    // true.
mutation(["Mary", "Aarmy"])                   // true.
mutation(["Alien", "line"])                   // true.
mutation(["floor", "for"])                    // true.
mutation(["hello", "neo"])                    // false.
*/

function mutation(arr) {

  // lower casing the arguments
  var word = arr[1].toLowerCase();
  var target = arr[0].toLowerCase();

  for (var i = 0; i < word.length; i++) {

    // if any element of first string does not exist in the second string return false else return true
    if (target.indexOf(word[i]) === -1) {
      return false;
    }
  }

  return true;
}