Merge Arrays in one with ES6 Array spread

gistfile1.txt

You can use this :

let arr1 = [1, 2, 3];
let arr2 = [4, 5, 6];

let concatAndDeDuplicate = (...arrs) => [ ...new Set( [].concat(...arrs) ) ];

concatAndDeDuplicate(arr1, arr2, [7, 8, 9, 2, 4]);
// [ 1, 2, 3, 4, 5, 6, 7, 8, 9 ]
And if you have multiple arrays of potentialy identical objects, you can use this :

Be aware that it's only taking into account the key you passed in your arguments to remove duplicates !

let arr1 = [
  { id: 6, username: 'lorem' },
  { id: 8, username: 'ipsum' }
];
let arr2 = [
  { id: 6, username: 'lorem' },
  { id: 7, username: 'dolor' }
];

let concatAndDeDuplicateObjects = (p, ...arrs) => [].concat(...arrs).reduce((a, b) => !a.filter(c => b[p] === c[p]).length ? [...a, b] : a, []);

concatAndDeDuplicateObjects('id', arr1, arr2);
/*
  [
    { id: 6, username: "lorem },
    { id: 8, username: 'ipsum' },
    { id: 7, username: 'dolor' }
  ]
*/
But if a deep comparison is mandatory to you, you can do this :

let arr1 = [
  { id: 6, username: 'lorem' },
  { id: 8, username: 'ipsum' }
];
let arr2 = [
  { id: 6, username: 'dolor' },
  { id: 7, username: 'sit' }
];

let concatAndDeDuplicateObjectsDeep = (p, ...arrs) => [ ...new Set( [].concat(...arrs).map(a => JSON.stringify(a)) ) ].map(a => JSON.parse(a))

concatAndDeDuplicateObjectsDeep('id', arr1, arr2);