Determine if an array of objects contains any object of another array in JavaScript

Question

Given the following two array objects:

let origArr = [ { value: 2, label: 'Dog' }, 
                { value: 4, label: 'Cat' },
                { value: 16, label: 'Horse' } 
              ]

let newArr = [
  { value: 2, label: 'Dog' },
  { value: 3, label: 'Bird' },
  { value: 0, label: 'Fish' }
]

what would be the best way to return a new array of just the value of the difference between the origArr and the newArr, that is, where origArr element(s) are not in newArr ?

In the above example, I am after a new array called diffArr = [4,16]

Please note: that all value values within both origArr and the newArr are unique

Not sure if there is an ES2016 means?

Does this answer your question? [How to get the difference between two arrays in JavaScript?](https://stackoverflow.com/questions/1187518/how-to-get-the-difference-between-two-arrays-in-javascript) of [How to get the difference between two arrays of objects in JavaScript](https://stackoverflow.com/questions/21987909/how-to-get-the-difference-between-two-arrays-of-objects-in-javascript/21988185) and [From an array of objects, extract value of a property as array](https://stackoverflow.com/questions/19590865/from-an-array-of-objects-extract-value-of-a-property-as-array) — pilchard, Oct 03 '21 at 08:15

Ran Turner · Accepted Answer · 2021-10-03T08:17:55.707

You can use filter and some to do the job.

let origArr = [ { value: 2, label: 'Dog' }, 
                { value: 4, label: 'Cat' },
                { value: 16, label: 'Horse' } 
              ]

let newArr = [
  { value: 2, label: 'Dog' },
  { value: 3, label: 'Bird' },
  { value: 0, label: 'Fish' }
]

const res = origArr.filter(x => !newArr.some(y => y.value === x.value));

console.log(res); // assuming you want the entire filtered objects

const justValues = res.map(x => x.value); // if you want just the filtered values

console.log(justValues)

some - https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/some

filter - https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/filter

might as well throw in the link to the duplicate as well https://stackoverflow.com/a/55316303/13762301 — pilchard, Oct 03 '21 at 08:17

score 0 · Answer 2 · answered Oct 03 '21 at 08:12

You can get all unique value from newArr using Set and array#map and then filter value which doesn't exist in the set and get all values.

const origArr = [ { value: 2, label: 'Dog' }, { value: 4, label: 'Cat' }, { value: 16, label: 'Horse' } ],
      newArr = [ { value: 2, label: 'Dog' }, { value: 3, label: 'Bird' }, { value: 0, label: 'Fish' } ],
      unique = new Set(newArr.map(o => o.value)),
      difference = origArr
            .filter(({value}) => !unique.has(value))
            .map(o => o.value);
console.log(difference);

Determine if an array of objects contains any object of another array in JavaScript

2 Answers2