JavaScript merging objects by id

Question

What\'s the correct way to merge two arrays in Javascript?

I\'ve got two arrays (for example):

var a1 = [{ id : 1, name : \"test\"}, { id : 2, name :         


        

Answer 1

Vanilla JS solution

const a1 = [{ id : 1, name : "test"}, { id : 2, name : "test2"}]
const a2 = [{ id : 1, count : "1"}, {id : 2, count : "2"}]

const merge = (arr1, arr2) => {
  const temp = []

  arr1.forEach(x => {
    arr2.forEach(y => {
      if (x.id === y.id) {
        temp.push({ ...x, ...y })
      }
    })
  })

  return temp
}

console.log(merge(a1, a2))

Answer 2

Already there are many great answers, I'll just add another one which is from a real problem I needed to solve yesterday.

I had an array of messages with user ids, and one array of users containing users' names and other details. This is how I managed to add user details to the messages.

var messages = [{userId: 2, content: "Salam"}, {userId: 5, content: "Hello"},{userId: 4, content: "Moi"}];
var users = [{id: 2, name: "Grace"}, {id: 4, name: "Janetta"},{id: 5, name: "Sara"}];

var messagesWithUserNames = messages.map((msg)=> {
  var haveEqualId = (user) => user.id === msg.userId
  var userWithEqualId= users.find(haveEqualId)
  return Object.assign({}, msg, userWithEqualId)
})
console.log(messagesWithUserNames)

Answer 3

reduce version.

var a3 = a1.concat(a2).reduce((acc, x) => {
    acc[x.id] = Object.assign(acc[x.id] || {}, x);
    return acc;
}, {});
_.values(a3);

I think it's common practice in functional language.

Answer 4

If you have exactly the same number of items in both array with same ids you could do something like this.

const mergedArr = arr1.map((item, i) => {
  if (item.ID === arr2[i].ID) {
    return Object.assign({}, item, arr2[i]);
  }
});

Answer 5

You can write a simple object merging function like this

function mergeObject(cake, icing) {
    var icedCake = {}, ingredient;
    for (ingredient in cake)
        icedCake[ingredient] = cake[ingredient];
    for (ingredient in icing)
        icedCake[ingredient] = icing[ingredient];
    return icedCake;
}

Next, you need to do use a double-loop to apply it to your data structre

var i, j, a3 = a1.slice();
for (i = 0; i < a2.length; ++i)                // for each item in a2
    for (j = 0; i < a3.length; ++i)            // look at items in other array
        if (a2[i]['id'] === a3[j]['id'])       // if matching id
            a3[j] = mergeObject(a3[j], a2[i]); // merge

You can also use mergeObject as a simple clone, too, by passing one parameter as an empty object.

Answer 6

function mergeDiffs(Schedulearray1, Schedulearray2) {
    var secondArrayIDs = Schedulearray2.map(x=> x.scheduleid);
    return Schedulearray1.filter(x=> !secondArrayIDs.includes(x.scheduleid)).concat(Schedulearray2);   
}