Sum all data in array of objects into new array of objects

Using for..in to iterate object and reduce to iterate array

var data = [{costOfAirtickets: 2500, costOfHotel: 1200},{costOfAirtickets: 1500, costOfHotel: 1000}];

var result = [data.reduce((acc, n) => {
  for (var prop in n) {
    if (acc.hasOwnProperty(prop)) acc[prop] += n[prop];
    else acc[prop] = n[prop];
  }
  return acc;
}, {})]
console.log(result)

Use Lodash to simplify your life.

const _ = require('lodash')
let keys = ['costOfAirtickets', 'costOfHotel']; 
let results = _.zipObject(keys, keys.map(key => _.sum( _.map(data, key))))
...
{ costOfAirtickets: 4000, costOfHotel: 2200 }

Explanation:

• _.sum(_.map(data, key)): generates sum of each array
• _.zipObject: zips the results with the array sum
• using keys.map() for sum of each key as _.map does not guarantee order.

Documentation:

• sum: https://lodash.com/docs/4.17.10#sum
• zipObject: https://lodash.com/docs/4.17.10#zipObject
• map: https://lodash.com/docs/4.17.10#map