Nodejs innerjoin

innerjoin.js

// See
// https://stackoverflow.com/questions/42429023/how-can-i-perform-an-inner-join-with-two-object-arrays-in-javascript#answer-42429128

const a = [
  {id: 4, name: 'Greg'},
  {id: 1, name: 'David'},
  {id: 2, name: 'John'},
  {id: 3, name: 'Matt'},
];

const b = [
  {id: 5, name: 'Mathew', position: '1'},
  {id: 6, name: 'Gracia', position: '2'},
  {id: 2, name: 'John', position: '2'},
  {id: 3, name: 'Matt', position: '2'},
];

const r = a.filter(({ id: idv }) => b.every(({ id: idc }) => idv !== idc));
const newArr = b.concat(r).map((v) => v.position ? v : { ...v, position: null });

console.log(JSON.stringify(newArr));

// Result
//[{"id":5,"name":"Mathew","position":"1"},{"id":6,"name":"Gracia","position":"2"},{"id":2,"name":"John","position":"2"},{"id":3,"name":"Matt","position":"2"},{"id":4,"name":"Greg","position":null},{"id":1,"name":"David","position":null}]