36 Factory Function

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

• The object is usually created using the new operator and a constructor function
• but the factory function abstracts this process and provides a more flexible and reusable way to create objects.

1. Simple Example

• In this example createPerson() function is a factory function
• Factory functions are useful for creating objects with a similar structure, as they provide a reusable way.

function createPerson(name, age) {
  return {
    name: name,
    age: age,
  };
}

const person1 = createPerson("John", 30);
const person2 = createPerson("Jane", 25);

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

2. Complex Example

• Here calculateTax is a factory function that holds reusable logic.
• When the createTaxCalculator is invoked it creates a new function of calculateTax and returns the same.

function createTaxCalculator(tax) {
  function calculateTax(amount) {
    return amount * tax;
  }
  return calculateTax;
}

const calculateVatAmount = createTaxCalculator(0.19);
const calculateIncomeTax = createTaxCalculator(0.23);

console.log(calculateVatAmount(100));
console.log(calculateIncomeTax(200));

3. Another Example

• The createPerson factory function takes name and age as arguments and returns an object with properties name, age, and a greet method.
• Each time the createPerson function is called, a new object is created with the specified properties and behavior.
• Factory functions encapsulate object creation logic, allowing us to define default values, apply data validation etc.
• It's flexible and expressive approach to create objects compared to constructor functions
• Especially when the creation process involves complexity or customization.
• Factory functions can be combined with other design patterns, such as the module pattern,
• to create powerful and modular code structures in JavaScript.

function createPerson(name, age) {
  return {
    name: name,
    age: age,
    greet: function() {
      console.log(`Hello, my name is ${this.name} and I'm ${this.age} years old.`);
    }
  };
}

const person1 = createPerson('John', 25);
const person2 = createPerson('Alice', 30);

person1.greet();  // Output: Hello, my name is John and I'm 25 years old.
person2.greet();  // Output: Hello, my name is Alice and I'm 30 years old.

Notes

• A factory function is a function that is designed to create and return objects.
• It is a pattern that allows you to encapsulate object creation logic and customize the properties or behavior of the objects being created.
• The main purpose of a factory function is to provide a convenient way to create multiple instances of similar objects without explicitly using the new keyword or constructor functions.