Factory Functions

A factory function is a function that creates and returns a new object.

Example

function createPerson(firstName, lastName) {
  return {
    firstName: firstName,
    lastName: lastName,
    getFullName() {
      return firstName + ' ' + lastName;
    },
  };
}

let person1 = createPerson('John', 'Doe');
let person2 = createPerson('Jane', 'Doe');

console.log(person1.getFullName()); // "John Doe"
console.log(person2.getFullName()); // "Jane Doe"

When you create an object, the JavaScript engine allocates memory to it. If you create many person objects, the JavaScript engine needs lots of memory spaces to store these objects.

Each person object has a copy of the same getFullName() method. It’s not efficient memory management.

To avoid duplicating the same getFullName() function in every object, you can use Object.create().

Object.create()

The Object.create() method creates a new object using an existing object as the prototype of the new object:

var personActions = {
  getFullName() {
    return this.firstName + ' ' + this.lastName;
  },
};

function createPerson(firstName, lastName) {
  let person = Object.create(personActions);
  person.firstName = firstName;
  person.lastName = lastName;
  return person;
}

let person1 = createPerson('John', 'Doe');
let person2 = createPerson('Jane', 'Doe');

console.log(person1.getFullName());
console.log(person2.getFullName());

Note: in practice, you will rarely use the factory functions. Instead, you use classes or constructor/prototype patterns.