//Adding two value of identical keys
const person = [
  {"1": 1},
  {"2":2},
  {"1": 3}
];

const newObj = {}
person.map(item=>{
    for(const [key, value] of Object.entries(item)){
        if(newObj[key]){
            newObj[key] = newObj[key] + item[key]
        }else{
            newObj[key]= value
        }
    }
})

console.log(newObj)