Best way to merge two objects on a matching key-value pair

Question

I'm having trouble making two objects into one on a matching key.

I have two objects coming from 2 apis and there is one matching key in the objects.

I want to iterate over them and if the storeId matches in both objects, I want to merge the two together as seen in the perfectObject.

I have tried the spread operator, Object.assign, for...in loop instead of the for loop seen here, but found close to none success.

Thanks for the help!

const logistics = [{
  logisticsId: "L5E69E26D8FCAE",
  storeId: 409388,
  logisticsDate: "2020-03-12T07:19:09.000Z",
}, ];

const stores = [{
  storeId: 409388,
  ka: 0,
  country: "ru",
  name: "test",
  city: "Moscow",
  cxw: 1,
  cx: 1,
  plz: 22448,
}, ];

const perfetObject = {
  storeId: 409388,
  ka: 0,
  country: "ru",
  name: "test",
  city: "Moscow",
  cxw: 1,
  cx: 1,
  plz: 22448,
  "storeId": 409388,
  logisticsId: "L5E69E26D8FCAE",
  storeId: 409388,
  logisticsDate: "2020-03-12T07:19:09.000Z",
};
"logisticsId": "L5E69E26D8FCAE",
let d = {};
}
for (let i = 0; i < logistics.length; ++i) {
  for (let k = 0; k < stores.length; ++k) {
    if (logistics.storeId === stores.storeId) {
      d = {
        ...stores.name,
        ...stores.city,
        ...logistics.logisticsId,
      };
    }
  }
  let d = {}

  console.log(d);

There are multiple errors in your code. Please make it runnable and edit the question again — DecPK
– DecPK, Commented Sep 15, 2021 at 13:37
What should happen if there is no counterpart in one of the arrays? — skyboyer
– skyboyer, Commented Sep 15, 2021 at 13:44

bburhans · Accepted Answer · 2021-09-15 13:46:12Z

Leaving aside the nested for loop (there are better data structures for you to take advantage of that make this unnecessary), the easiest method would be to use Object.assign() or the spread operator, especially if the key names are guaranteed to never conflict.

const logistics = [{
  logisticsId: "L5E69E26D8FCAE",
  storeId: 409388,
  logisticsDate: "2020-03-12T07:19:09.000Z",
}, ];

const stores = [{
  storeId: 409388,
  ka: 0,
  country: "ru",
  name: "test",
  city: "Moscow",
  cxw: 1,
  cx: 1,
  plz: 22448,
}, ];

for (let i = 0; i < logistics.length; ++i) {
  for (let k = 0; k < stores.length; ++k) {
    if (logistics[i].storeId === stores[k].storeId) {
      console.log(Object.assign({}, logistics[i], stores[k]));
    }
  }
}

This assumes all store IDs are valid (e.g. have the expected store data) and all logistics elements have a valid store defined.

GoOsT · Accepted Answer · 2021-09-15 13:37:50Z

This is a working example answer from a reddit user u/albedoa:

const storesByStoreId = stores.reduce(
  (obj, store) => {
    if (!obj.hasOwnProperty(store.storeId)) {
      obj[store.storeId] = store;
    }

    return obj;
  },
  {}
);

const perfectArray = logistics.map(logistic => ({
  ...storesByStoreId[logistic.storeId],
  ...logistic
}));

This way, it combines the two as supposed to, or returns the object itself if there is no match.

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