Object.assign()

Object.assign() is a method in JavaScript that is used to copy the values of all enumerable properties from one or more source objects to a target object. It returns the target object with the updated properties.

Syntax

Object.assign(target, source);
Object.assign(target, source1, source2, source3, ...sourceN);

Parameter

• target: The first parameter is the target object that will be updated with the properties of the source object(s). This parameter is mandatory.
• sources: One or more source objects that will be used to update the target object. If there are multiple sources, they will be applied in order from left to right. This parameter is also mandatory.

Return Value

Object.assign() returns the target object with the updated properties.

Examples

Example 1: Merging two objects into a new object

const obj1 = { name: "John" };
const obj2 = { age: 25 };
const obj3 = Object.assign({}, obj1, obj2);
console.log(obj3); // Output: { name: "John", age: 25 }

Example 2: Updating an existing object

const obj1 = { name: "John", age: 25 };
const obj2 = { age: 30 };
Object.assign(obj1, obj2);
console.log(obj1); // Output: { name: "John", age: 30 }

Example 3: Copying an object with nested properties

const obj1 = {
  name: "John",
  address: {
    street: "123 Main St",
    city: "New York",
  },
};
const obj2 = Object.assign({}, obj1);
console.log(obj2);
// Output: {
//   name: "John",
//   address: {
//     street: "123 Main St",
//     city: "New York"
//   }
// }

Notes

• The method only copies the enumerable properties of the source object(s) to the target object. If a property is non-enumerable, it will not be copied.
• The method copies property values by reference. This means that if the property value is an object or an array, the target object will have a reference to the same object/array as the source object. Any changes made to the original object/array will also be reflected in the copied object.
• If the same property exists in both the target and source objects, the property value in the target object will be overwritten by the value in the source object.

Exercises

1. Create a function mergeObjects that takes in two objects as parameters and returns a new object that contains all the properties from both objects. Use Object.assign() to implement the function.
2. Create an object person with the properties name, age, and address. Create a copy of this object and store it in a variable personCopy using Object.assign(). Update the age property in the personCopy object to be 30. Print both the person and personCopy objects to the console and verify that only the age property in personCopy has changed.
3. Create an object book with the properties title, author, and publisher. Create an object bookDetails with the properties genre and year. Use Object.assign() to copy all properties from bookDetails to book. Print the book object to the console to verify that the properties from bookDetails

function mergeObjects(obj1, obj2) {
  return Object.assign({}, obj1, obj2);
}

const obj1 = { name: "John" };
const obj2 = { age: 25 };
const obj3 = mergeObjects(obj1, obj2);
console.log(obj3); // Output: { name: "John", age: 25 }

const person = {
  name: "John",
  age: 25,
  address: {
    street: "123 Main St",
    city: "New York",
  },
};

const personCopy = Object.assign({}, person);
personCopy.age = 30;

console.log(person); // Output: { name: "John", age: 25, address: { street: "123 Main St", city: "New York" } }
console.log(personCopy); // Output: { name: "John", age: 30, address: { street: "123 Main St", city: "New York" } }

const book = {
  title: "The Great Gatsby",
  author: "F. Scott Fitzgerald",
  publisher: "Scribner",
};

const bookDetails = {
  genre: "Fiction",
  year: 1925,
};

Object.assign(book, bookDetails);

console.log(book);
// Output: {
//   title: "The Great Gatsby",
//   author: "F. Scott Fitzgerald",
//   publisher: "Scribner",
//   genre: "Fiction",
//   year: 1925
// }