How to do a join from 2 JSON by a common ID field in Javascript

I have two JSON files: JSON A has some company properties and the company_id, while JSON B has company names and company ids.

JSON A example:

[
  {
    "order_name": "Foo",
    "company_id": "112233"
  },
  {
    "order_name": "Bar",
    "company_id": "123456"
  }
]

JSONB example:

[
  {
     "company_id":"112233",
     "name":"ACME company",
  },
  {
     "company_id":"123456",
     "name":"John Doe Inc.",
  }
]

Which is the most efficient way to do a join by the company_id values? I would like to have the JSON C (merged result) with the company names correctly added, like this:

[
  {
    "order_name": "Foo",
    "company_id": "123456",
    "company_name": "John Doe Inc."
  },
  {
    "order_name": "Bar",
    "company_id": "112233",
    "company_name": "ACME company"
  }
]

Is looping and filter for each the only solution? Is there a more efficient way to do this from a performance point of view?

More info:

• JSON is not sorted by company_id.
• Array A could have more than one object with the same company_id
• I’m using Javascript (in a Vue.js app), I don’t need to support old browsers

Answer

In common modern JavaScript, you can do this as you mentioned with higher-order functions like map, filter, and so on:

const arrayA = [
  {
    "order_name": "Foo",
    "company_id": "112233"
  },
  {
    "order_name": "Bar",
    "company_id": "123456"
  }
]

const arrayB = [
  {
     "company_id":"112233",
     "name":"ACME company",
  },
  {
     "company_id":"123456",
     "name":"John Doe Inc.",
  }
]

const mergeAB = arrayA.map( companyA => {
    const matched = arrayB.find(companyB => companyB.company_id === companyA.company_id)
    if(matched) {
      return {...companyA, ...matched}
    } else {
      // return companyA element or customize it with your case
    }
  }
)

console.log(mergeAB)

Note 1: Array.find() method complexity is O(n) and Array.map() method complexity is O(n)

Note 2: efficiency is an important thing but not in all situations. sometimes you need to do these types of iteration one time or for a small array size, so no need to worry about the performance.

Note 3: you could compare the answer and find out your best solution since we don’t know about your whole code and application.