Merge two objects in javascript ignoring undefined values

Question

I have to merge two objects but I don't want to assign undefined value to defined values.

A = { activity: 'purchased', count: undefined, time: '09:05:33' }
B = { activity: 'purchased', count: '51', time: undefined }

When I try Object.assign, undefined is replacing fields that have values.

What I want

C = { activity: 'purchased', count: '51', time: '09:05:33' }

first remove the undefined `Object.keys(A).filter(key => A[key]).reduce((acc, key) => (acc[key] = A[key], acc), {})` ones and assign. — Kharel, Jul 10 '20 at 16:02
Will `A` and `B` have same property name (i.e no extra property in any of them) and can `A` and `B` have different values of same property? If yes, them which one to assign. — kapil pandey, Jul 10 '20 at 16:08
I cleaned up the tags but kept the _reactjs_ tag as I guess it's because you're looking for an immutable solution? — Emile Bergeron, Jul 10 '20 at 17:59

Arun Saini · Answer 1 · 2020-07-10T18:38:23.673

4

The spread operator(...) works well to merge objects, and there is a simple solution to remove undefined using JSON.stringify() and JSON.parse(). See below example:

const A = { activity: 'purchased', count: undefined, time: '09:05:33' };
const B = { activity: 'purchased', count: '51', time: undefined };

//If you don't care about date objects then only use below method 
const C = {...JSON.parse(JSON.stringify(A)), ...JSON.parse(JSON.stringify(B))};

console.log(C);

edited Jul 10 '20 at 18:38

answered Jul 10 '20 at 17:46

Arun Saini

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This won't work with a variety of other values ([anything that's not JSON serializable](https://stackoverflow.com/a/122704/1218980)), so be careful. – Emile Bergeron Jul 10 '20 at 17:58

kapil pandey · Answer 2 · 2020-07-10T16:17:30.147

3

let A = { activity: 'purchased', count: undefined, time: '09:05:33' }
let B = { activity: 'purchased', count: '51', time: undefined }

let C={}
Object.keys({...A,...B}).map(key=>{
C[key]=B[key]||A[key]
})
console.log(C)

edited Jul 10 '20 at 16:17

answered Jul 10 '20 at 15:59

kapil pandey

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You lose eventualy additional attributes of B – MadPapo Jul 10 '20 at 16:00
I am considering `A` and `B` both have same properties – kapil pandey Jul 10 '20 at 16:02
So it is not perfect...This is not a complete merge. But it is based only on A structure – MadPapo Jul 10 '20 at 16:03
I have updated the solution to be a complete merge now. But still the question is vage. What is same property have different values, then which one to be considered. – kapil pandey Jul 10 '20 at 16:06
This will replace all other falsy values in B with anything that's in A. – Emile Bergeron Jul 10 '20 at 17:30

score 3 · Answer 3 · answered Jan 10 '22 at 23:37

3

You could use lodash's merge command. C = _.merge(A,B);

answered Jan 10 '22 at 23:37

TPoschel

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score 0 · Answer 4 · answered Jul 10 '20 at 17:24

You could merge the objects by having a look to the entries of the second object and take only key/value pairs without undefined as value.

const
    merge = (a, b) => Object.assign(
        {},
        a,
        ...Object.entries(b).map(([k, v]) => v === undefined ? {} : { [k]: v })
    ),
    a = { activity: 'purchased', count: undefined, time: '09:05:33' },
    b = { activity: 'purchased', count: '51', time: undefined };

console.log(merge(a, b));

score -2 · Answer 5 · answered Jul 10 '20 at 15:59

const A = { activity: 'purchased', count: undefined, time: '09:05:33' }
const B = { activity: 'purchased', count: '51', time: undefined }
const AKeys = Object.keys(A);
const BKeys = Object.keys(B);
const C = {};
AKeys.forEach(element=>A[element] && C[element]=A[element])
BKeys.forEach(element=>B[element] && C[element]=B[element])

fedesc · Answer 6 · 2020-07-10T17:12:14.363

-2

let A = { activity: 'purchased', count: undefined, time: '09:05:33' }
let B = { activity: 'purchased', count: '51', time: undefined }

for (let a in A) {
  if (A[a] === undefined) 
    delete A[a];
}

for (let b in B) {
  if (B[b] === undefined) 
    delete B[b];
}

let c = {...A, ...B} // this will merge identical key/values

console.log(c)

edited Jul 10 '20 at 17:12

answered Jul 10 '20 at 16:07

fedesc

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Merge two objects in javascript ignoring undefined values

6 Answers6