sets and array difference in ES6

1.js

// initial set created from array
var mySet = new Set([1, 2, 3, 2, 4, 1, 3, 5]);

// add more items
mySet.add(1);
mySet.add(3);

// see what it holds
console.log(mySet); // => Set { 1, 2, 3, 4, 5 }

2.js

var completeList = [/* ... filled in elsewhere */]

var invalidList = [/* ... also filled in elsewhere */]

// filter the items from the invalid list, out of the complete list
var validList = completedList.filter((item) => {
  return !invalidList.has(item);
})

// get a Set of the distinct, valid items
var validItems = new Set(validList);

Small typo in 2.js...

var validList = completedList.filter((item) should be

var validList = completeList.filter((item)

Hope this modified version helps :)

var completedList = [1,2,3,4];
var invalidList = new Set([3,4,5,6]);
// filter the items from the invalid list, out of the complete list
var validList = completedList.filter((item) => {
  return !invalidList.has(item);
})
console.log(validList);