How to copy the data of one object to another object and perform subtraction of 2 object's values in javascript?

Question

I have a use case in which I need to copy the whole object data to another object without creating an inner object. i.e, object inside the object.

For example,

obj_1 = {
       "_id": "SPool",
       "w1": 60,
       "w2": 150
     }

obj_2 = {
        "_id": "SPool",
        "w1": 30,
        "w2": 120
      }

As both objects having same _id fields, I want to copy the data of obj-2 to obj-1 and want to find the difference between the 2 objects like the following.

obj_1 = {
       "_id": "SPool",
       "w1": 60,
       "w2": 150,
       "obj_2" : {
                   "w1": 30,
                   "w2": 120
                 }
       "diff": {
                 "w1": 30,
                 "w2": 30
               }
     }

Is it possible to do like this?

Thanks for letting me know @Daniyal Lukmanov. I'm shocked, how did I forget this. Thanks once again. — Aravind, Feb 10 '20 at 10:22
i think this might help you !! https://stackoverflow.com/a/18884871/10967697 — Engineer S. Saad, Feb 10 '20 at 10:23
It can be done pretty simple with `array.reduce` method or even simplier. Have you tried that? — Daniyal Lukmanov, Feb 10 '20 at 10:32

Terry Lennox · Accepted Answer · 2020-02-10T10:46:18.880

2

You should be able to use Array.reduce, Object.entries etc. to create the new, merged object from the "parent" objects.

obj_1 = {
       "_id": "SPool",
       "w1": 60,
       "w2": 150
     }

obj_2 = {
        "_id": "SPool",
        "w1": 30,
        "w2": 120
      }
      
 function mergeObjects(obj_1, obj_2, propertyName) {
     let merged = { ...obj_1 };
     merged[propertyName] = obj_2;
     merged.diff = Object.entries(obj_1).reduce((acc, [key, value]) => { 
         if (obj_2[key] && typeof obj_2[key] === "number") { 
             acc[key] = value - obj_2[key];
         }
         return acc;
     }, {});
     return merged;
 }
 

 console.log("Merged objects:", mergeObjects(obj_1, obj_2, "obj_2"));

edited Feb 10 '20 at 10:46

answered Feb 10 '20 at 10:44

Terry Lennox

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I don't know to which extent this is important for OP, but he specifies ```obj_1``` to be modified, which here is not the case, ```obj_1``` is left intact. – grodzi Feb 10 '20 at 11:12
1

HI @grodzi, thank you very much for the comment. You're right that we do not modify obj_1, rather we clone it and assign obj2 as a child of the cloned object. I rather think that in general this is a better pattern, i.e, effectively immutable objects. But you could easily change this behaviour by replacing let merged = { ...obj_1 } with let merged = obj_1. – Terry Lennox Feb 10 '20 at 11:16

How to copy the data of one object to another object and perform subtraction of 2 object's values in javascript?

1 Answers1