ES6: Set, Map.js

var alpha = 'dajvgiasdrrrrkq;wrklrq';

var Letters = new Map();

// has set get methods
alpha.split('').map(letter => {
  if (!Letters.has(letter)) Letters.set(letter, 1);
  else Letters.set(letter, Letters.get(letter) + 1);
});
// keys() values() and entries() contain both.
var iterator1 = Letters.keys();
var iterator2 = Letters.values();
var iterator3 = Letters.entries();
console.log(iterator2.next());

// { value: 'd', done: false }
// { value: 2, done: false }
// { value: [ 'd', 2 ], done: false }
console.log(Letters);
/*
 => Map {
  'd' => 2,
  'a' => 2,
  'j' => 1,
  'v' => 1,
  'g' => 1,
  'i' => 1,
  's' => 1,
  'r' => 6,
  'k' => 2,
  'q' => 2,
  ';' => 1,
  'w' => 1,
  'l' => 1 }   
*/

// entries needs two variables 
for(let [key,value] of Letters.entries()){
  console.log([key,value]);
}
// keys() values() need one variable
for(let i of Letters.values()){
  console.log(i);
}



// delete and clear methods
// delete 'r'
Letters.delete('r');
// clean all in map
Letters.clear();





var arr = [1, 2, 3, 7, 3, 8, 4];

var set = new Set(arr);
console.log(set);
// Set { 1, 2, 3, 7, 8, 4 }

set.add(5);
set.has(0); // false

// delete and clear methods
set.delete(5);
// set.clear();

// for...in is nothing to do at Set
for (let i of set) {
  console.log(i);
}// 1 2 3 7 8 4

for (let i of set.values()) {
  console.log(i);
}// same
for (let i of set.keys()) {
  console.log(i);
}// same

for (let i of set.entries()) {
  console.log(i);
}
/*
[ 1, 1 ]
[ 2, 2 ]
[ 3, 3 ]
[ 7, 7 ]
[ 8, 8 ]
[ 4, 4 ]
*/

var iterator1 = set.keys();
var iterator2 = set.values();
var iterator3 = set.entries();
console.log(iterator3.next());
// { value: 1, done: false }
// { value: 1, done: false }
// { value: [ 1, 1 ], done: false }

both of them cannot use the for...in loop