How to Merge Multiple Objects in TypeScript (2 Approaches)

Updated: December 3, 2023 By: Khue Post a comment

This quick article shows you 2 different approaches to merging 2 or more objects in TypeScript. Without any further ado, let’s get our hands dirty by writing some code.

Table Of Contents

1 Using the spread operator

2 Using the Object.assign() method

Using the spread operator

There are some important things you need to keep in mind:

By using the spread syntax (...), the type of the merged object will be inferred automatically. TypeScript will yell at you if you are intent on adding/removing properties to/from the final object (it’s fine if you just want to update the values of the properties).

The order of the objects is important. If objects have duplicate keys, only the values corresponding to those keys of the last object will be retained

Example:

const objectOne = {
  name: 'Product One',
  price: 100,
  description: 'This is product one',
};

const objectTwo = {
  weight: 100,
  color: 'red',
};

const objectThree = {
  name: 'Product Three',
  descriptioN: 'Some dummy description',
  color: 'blue',
};

// merging objectOne and objectTwo
const a = { ...objectOne, ...objectTwo };
console.log(a);

// merging three objects
// the last object will override the previous objects
const b = { ...objectOne, ...objectTwo, ...objectThree };
console.log(b);

Output:

// console.log(a);
{
  name: 'Product One',
  price: 100,
  description: 'This is product one',
  weight: 100,
  color: 'red'
}

// console.log(b);
{
  name: 'Product Three',
  price: 100,
  description: 'This is product one',
  weight: 100,
  color: 'blue',
  descriptioN: 'Some dummy description'
}

If you hover your mouse over one of the results, you’ll see it type:

Using the Object.assign() method

This approach works almost the same as the previous one.

Example:

const objectOne = {
  name: 'Product One',
  price: 100,
  description: 'This is product one',
};

const objectTwo = {
  weight: 100,
  color: 'red',
};

const objectThree = {
  name: 'Product Three',
  descriptioN: 'Some text',
  color: 'blue',
};

// Merge objectOne and objectTwo by using Object.assign()
const resultOne = Object.assign({}, objectOne, objectTwo);
console.log(resultOne);

// Merge objectOne, objectTwo, and objectThree by using Object.assign()
const resultTwo = Object.assign({}, objectOne, objectTwo, objectThree);
console.log(resultTwo);

Output:

// console.log(resultOne);
{
  name: 'Product One',
  price: 100,
  description: 'This is product one',
  weight: 100,
  color: 'red'
}

// console.log(resultTwo);
{
  name: 'Product Three',
  price: 100,
  description: 'This is product one',
  weight: 100,
  color: 'blue',
  descriptioN: 'Some text'
}

TypeScript is smart and is capable of inferring the types of the results, as you can see in the screenshot below: