JavaScript: How to merge two object but keep only the property of the second object if it exists?

Question

This code merges two objects. How to amend it so that a property is discarded of the first object if it exists in the second object?

E.g. object 1 has this property:

surname: { test: '123', other: '124' },

and object 2:

surname: { test: '124' },

The merge would use the property of object 2 (other: '124' would not exist in the merged result)

function merge(...objects) { function m(t, s) { Object.entries(s).forEach(([k, v]) => { t[k] = v && typeof v === 'object' ? m(t[k] || {}, v) : v; }); return t; } return objects.reduce(m, {}); } var obj1 = { name: '112', surname: { test: '123', other: '124' }, age: 151, height: '183', weight: 80 }, obj2 = { name: '114', surname: { test: '124' }, age: 151, height: 184, weight: 81 }, result = merge(obj1, obj2); console.log(result);

did you check this link stackoverflow.com/questions/50176456/…? The function should have a deep merge or a simple merge of two objects? — kstepien
– kstepien, Commented Jun 14, 2022 at 6:07
Thanks, $.extend(obj1, obj2) is what I had been looking for! The merge performed by $.extend() is not recursive by default; if a property of the first object is itself an object or array, it will be completely overwritten by a property with the same key in the second or subsequent object. The values are not merged. — smolo
– smolo, Commented Jun 14, 2022 at 6:18

monirshimul · Accepted Answer · 2022-06-14 06:26:37Z

8

const a = { x:1, y:2} const b = { x:5 } const c = { ...a, ...b } console.log(c) // Answer will be {x: 5, y: 2}

answered Jun 14, 2022 at 6:26

monirshimul

1045 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Gabriele Petrioli · Accepted Answer · 2022-06-14 06:25:26Z

You seem to want to do a shallow merge but with recreated objects to avoid references to the original ones.

A quick way for this is to use Object.assign for the merge, and then do a json stringify/parse (with the limitations of what JSON supports) to clone the result and lose the references (you could alternatively use structuredCloned if your environment/browser supports it).

So something like

function merge(...objects) { const shallowClone = Object.assign({}, ...objects); const asString = JSON.stringify(shallowClone); const asObject = JSON.parse(asString); return asObject; }

It seems to works as intended. However, it is hard to tell what the difference is to monirshimul's solution, which seems simpler to me
@smolo that answer has only the shallow merge part. So it is keeping the original object references. If you do, after the merge, obj2.surname.test = "new" it will affect the result vairable as well.

Collectives™ on Stack Overflow

JavaScript: How to merge two object but keep only the property of the second object if it exists?

2 Answers 2

Comments

2 Comments

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

2 Comments

Linked

Related