1let intersection = arrA.filter(x => arrB.includes(x));

1const arr1 = [{ id: 1 }, { id: 2 }]
2const arr2 = [{ id: 1 }, { id: 3 }]
3const intersection = arr1.filter(item1 => arr2.some(item2 => item1.id === item2.id))
4// intersection => [{ id: 1 }]

1const intersection = (a, b) => {
2  b = new Set(b); // recycling variable
3  return [...new Set(a)].filter(e => b.has(e));
4};
5
6console.log(intersection([1, 2, 3, 1, 1], [1, 2, 4])); // Array [ 1, 2 ]

1// Generic helper function that can be used for the three operations:        
2const operation = (list1, list2, isUnion = false) =>
3    list1.filter(
4        (set => a => isUnion === set.has(a.userId))(new Set(list2.map(b => b.userId)))
5    );
6
7// Following functions are to be used:
8const inBoth = (list1, list2) => operation(list1, list2, true),
9      inFirstOnly = operation,
10      inSecondOnly = (list1, list2) => inFirstOnly(list2, list1);
11
12// Sample data
13const list1 = [
14    { userId: 1234, userName: 'XYZ'  }, 
15    { userId: 1235, userName: 'ABC'  }, 
16    { userId: 1236, userName: 'IJKL' },
17    { userId: 1237, userName: 'WXYZ' }, 
18    { userId: 1238, userName: 'LMNO' }
19];
20const list2 = [
21    { userId: 1235, userName: 'ABC'  },  
22    { userId: 1236, userName: 'IJKL' },
23    { userId: 1252, userName: 'AAAA' }
24];
25  
26console.log('inBoth:', inBoth(list1, list2)); 
27console.log('inFirstOnly:', inFirstOnly(list1, list2)); 
28console.log('inSecondOnly:', inSecondOnly(list1, list2));