JSFiddle - React, Tailwind, and code Playground

JavaScript

var t1 = {
  a: 12,
  b: 8,
  c: 17
}

var t2 = {
  a: 2,
  b: 4,
  c: 1
}

function sum(ob1, ob2) {
  let sum = {};
  
  Object.keys(ob1).forEach(key => {
    if (ob2.hasOwnProperty(key)) {
      sum[key] = ob1[key] + ob2[key]
    }  
  })
  return sum;
}

console.log(sum(t1, t2))