Is there an easy way to merge objects and sum their int properties instead of overriding in javascript es2018? [duplicate]

Question

Alright, so this is what I have in mind.

I have two example objects

let obj1 = { x: 60 };

let obj2 = { x: 9 };

I want to merge these objects in a way that their integer properties will combine as well, and not override each other, so the end result will be

let obj3 = { x: 69 };

So I've looked into Object.assign, but this function only merges properties in a way that it favors the properties on the first object if the other objects have a property with the same name, and doesn't sum integer properties.

I can, of course, just make a function that loops over each object's properties and creates a new object with the summed properties, but that'd be longer and I wanted to know if there's already a function that does it easily like the way Object.assign acts.

Thank you.

Answer 1

If you want to use Lodash library you could do this with mergeWith method.

let obj1 = { x: 60, b: "foo", c: {y: 3, x: 'bar'} };
let obj2 = { x: 9, a: 'bar', c: {y: 4} };

const sum = _.mergeWith(obj1, obj2, (a, b) => {
  if (_.every([a, b], _.isNumber)) return a + b;
})

console.log(sum)

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.10/lodash.js"></script>

Answer 2

You could reduce the objects by taking an arbitrary count of objects and reduce the key/value pairs by respecting nested objects.

const
    add = (...a) => a                         // take all parameters
        .map(Object.entries)                  // get entries
        .reduce((a, b) => [...a, ...b], [])   // flat entries
        .reduce((o, [k, v]) => {
            o[k] = v && typeof v === 'object' // assign if object
                ? add(o[k] || {}, v)          //   result of recursive call
                : (o[k] || 0) + v;            //   or sum the value
            return o;
        }, {});

let obj1 = { x: 60, y: { z: 3 } },
    obj2 = { x: 9, y: { z: 1, a: 32 } },
    obj3 = { y: { a: 10 } },
    result = add(obj1, obj2, obj3);

console.log(result);

.as-console-wrapper { max-height: 100% !important; top: 0; }