Factory Pattern
Use a factory function in order to create objects
Overview
With the Factory Pattern, we can use a special function - the factory function - to create many of the same objects.
Implementation
A factory function can be any function that returns an object.
factory-pattern.js
const createUser = (firstName, lastName) => ({
id: crypto.randomUUID(),
createdAt: Date.now(),
firstName,
lastName,
fullName: `${firstName} ${lastName}`,
});
createUser("John", "Doe");
createUser("Sarah", "Doe");
createUser("Lydia", "Hallie");
Tradeoffs
✔ DRY The factory pattern is useful when we have to create multiple
objects that share the same properties, without having to repeat the same code
over and over. A factory function can easily return a custom object depending
on the current environment, or user-specific configuration.
⚠️ Not Really a Pattern In JavaScript, the factory pattern isn't much more than a function that returns an object without using the new keyword. ES6 arrow functions allow us to create small factory functions that implicitly return an object each time.However, in many cases it may be more memory efficient to create new instances instead of new objects each time.
user.js
The class User {
constructor(firstName, lastName, email) {
this.firstName = firstName;
this.lastName = lastName;
this.email = email;
}
async getPosts() {
const posts = await fetch(`https://my.cms.com/posts/user/${this.id}`);
return posts;
}
}
const user1 = new User({
firstName: "John",
lastName: "Doe",
email: "john@doe.com",
});
const user2 = new User({
firstName: "Jane",
lastName: "Doe",
email: "jane@doe.com",
});
fullName
method is the same for all the objects that were created. By creating new instances, the fullName
method is available on the prototype instead of on the objec, which saves memory.Exercise
Challenge
Refactor the following code to use a createBook
factory function.