JSFiddle - React, Tailwind, and code Playground

Babel + JSX

let obj1 = {
	'34123812371293': 2,
  '12314981391230': 3,
}
let obj2 = {
	'13812381238123' : 1,
	'19312930812930' : 3,
  '12314981391230': 100,
}

let combinedObj = Object.assign({}, obj1);
Object.keys(obj2).map(o2 => {
	if(combinedObj[o2] != undefined){
  	combinedObj[o2] += obj2[o2];
  }else{
  	combinedObj[o2] = obj2[o2];
  }
});
console.log(combinedObj);