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javascriptsum

How can I sum properties from two objects?

I have multiple JavaScript objects:

{
  a: 12,
  b: 8,
  c: 17
}

and

{
  a: 2,
  b: 4,
  c: 1
}

I need to sum these two object by keys

Result:

{
  a: 14,
  b: 12,
  c: 18
}

Do you have any solutions in JavaScript? I use Object.keys.map but it's too long because I have like 100 elements in my object.

Solution

  • You can use reduce for that, below function takes as many objects as you want and sums them by key:

    var obj1 = {
  a: 12,
  b: 8,
  c: 17
};

var obj2 = {
  a: 12,
  b: 8,
  c: 17
};

var obj3 = {
  a: 12,
  b: 8,
  c: 17
};


function sumObjectsByKey(...objs) {
  return objs.reduce((a, b) => {
    for (let k in b) {
      if (b.hasOwnProperty(k))
        a[k] = (a[k] || 0) + b[k];
    }
    return a;
  }, {});
}

console.log(sumObjectsByKey(obj1, obj2, obj3));