JavaScript: add new property to array elements according to another array

Question

I have two arrays.

When comparing, if arr1 property id matches with arr2 property id, then add new property tag: assign else add tag: ''

I have tried the below code:

var result = arr1.filter(({ id: id }) => 
  !arr2.some(({ name: name }) => name === id)
);

Sample inputs:

var arr1 = [
  {id:1, name: "ram"},
  {id:24, name: "zen"},
  {id: 3, name: "sam"}
]
var arr2 = [
  {id:24, name: "zen"},
  {id: 3, name: "sam"}
]

Expected Output:

 [
  {id:1, name: "ram", tag:''},
  {id:24, name: "zen", tag: 'yes'},
  {id: 3, name: "sam", tag: 'yes'}
]

also: [JavaScript merging objects by id](https://stackoverflow.com/questions/19480008/javascript-merging-objects-by-id) — pilchard, Feb 12 '22 at 15:01
The duplicate assigned is for merging arrays, not what OP is looking for. — Majed Badawi, Feb 12 '22 at 15:14

score -1 · Answer 1 · answered Feb 12 '22 at 15:04

Create a Set of ids in arr2 using Array#map
Again, using Array#map, iterate over arr1 and set tag using Set#has

const 
  arr1 = [ {id:1, name: "ram"}, {id:24, name: "zen"}, {id: 3, name: "sam"} ],
  arr2 = [ {id:24, name: "zen"}, {id: 3, name: "sam"} ];
  
const arr2IdsSet = new Set( arr2.map(({ id }) => id) );

const res = arr1.map(e => ({ ...e, tag: arr2IdsSet.has(e.id) ? 'yes' : '' }));

console.log(res);

JavaScript: add new property to array elements according to another array

1 Answers1