TypeScript Factory Method Example

This post shows how to use the Factory Method Pattern in TypeScript with an example. 

The factory method is a creational design pattern that solves the problem of creating product objects without specifying their concrete classes.

Factory Method Structure

Factory Method Example

Let's define an interface for creating an object, but let subclasses decide which class to instantiate. Factory Method lets a class defer instantiation to subclasses.

Let's create a file named "factory-method.ts" and add the following code to it:

interface Product {
    doSomething(): void;
}

interface Factory {
    createProduct(name: string): Product;
}

class ConcreteProductA implements Product {
    doSomething(): void {
        console.log('Product A do this');
    }
}

class ConcreteProductB implements Product {
    doSomething(): void {
        console.log('Product B do this');
    }
}

class ConcreteProductC implements Product {
    doSomething(): void {
        console.log('Product C do this');
    }
}

class ProductFactory implements Factory {
    createProduct(name: string): Product {
        switch (name) {
            case 'product-a':
                return new ConcreteProductA();
            case 'product-b':
                return new ConcreteProductB();
            case 'product-c':
                return new ConcreteProductC();
            default:
                return null;
        }
    }
}

(function main() {
    const factory = new ProductFactory();
    const productA = factory.createProduct('product-a');
    productA.doSomething();

    const productB = factory.createProduct('product-b');
    productB.doSomething();

    const productC = factory.createProduct('product-c');
    productC.doSomething();
})()

Run:

1. Compile the above code using the TypeScript compiler.
2. Above code is compiled to plan JavaScript code
3. Run Javascript code using node

C:\typescript-design-patterns\factory-method> tsc .\factory-method.ts
C:\typescript-design-patterns\factory-method> node .\factory-method.js

Output:

Product A do this
Product B do this
Product C do this

The above "factory-method.ts" file compiled into below plan JavaScript code by TypeScript compiler:

var ConcreteProductA = /** @class */ (function () {
    function ConcreteProductA() {
    }
    ConcreteProductA.prototype.doSomething = function () {
        console.log('Product A do this');
    };
    return ConcreteProductA;
}());
var ConcreteProductB = /** @class */ (function () {
    function ConcreteProductB() {
    }
    ConcreteProductB.prototype.doSomething = function () {
        console.log('Product B do this');
    };
    return ConcreteProductB;
}());
var ConcreteProductC = /** @class */ (function () {
    function ConcreteProductC() {
    }
    ConcreteProductC.prototype.doSomething = function () {
        console.log('Product C do this');
    };
    return ConcreteProductC;
}());
var ProductFactory = /** @class */ (function () {
    function ProductFactory() {
    }
    ProductFactory.prototype.createProduct = function (name) {
        switch (name) {
            case 'product-a':
                return new ConcreteProductA();
            case 'product-b':
                return new ConcreteProductB();
            case 'product-c':
                return new ConcreteProductC();
            default:
                return null;
        }
    };
    return ProductFactory;
}());
(function main() {
    var factory = new ProductFactory();
    var productA = factory.createProduct('product-a');
    productA.doSomething();
    var productB = factory.createProduct('product-b');
    productB.doSomething();
    var productC = factory.createProduct('product-c');
    productC.doSomething();
})();

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