Builder Method | JavaScript Design Pattern

The Builder design pattern is a creational design pattern used to construct complex objects by separating the construction process from the actual representation. It’s especially useful when an object requires multiple steps or configurations to be created.

Example without using the Builder Design Pattern

Let us take an example without using the Builder Design Pattern:

Javascript

class User {
  constructor(name , age , weight , address , gender) {
    this.name = name;
    this.age = age;
    this.weight = weight;
    this.address = address;
    this.gender = gender;
  }
  printUser() {
    return `User: { name: ${this.name}, age: ${this.age}, weight: ${this.weight}, address: ${this.address}, gender: ${this.gender} }`;
  }
}

const user  = new User('Abhishek' , 22 , 55 , 'India' , 'Male' );
console.log(user.printUser());

Explanation of the above example:

User Class Definition:

Javascript

class User {
  constructor(name, age, weight, address, gender) {
    this.name = name;
    this.age = age;
    this.weight = weight;
    this.address = address;
    this.gender = gender;
  }
  printUser() {
    return `User: { name: ${this.name}, age: ${this.age}, weight: ${this.weight}, address: ${this.address}, gender: ${this.gender} }`;
  }
}

• The User class is defined with a constructor that takes parameters for the user’s name, age, weight, address, and gender. The constructor initializes the respective attributes.
• The printUser method generates a formatted string representing the user’s information.

Creating a User Instance:

const user = new User('Abhishek', 22, 55, 'India', 'Male');

This line creates an instance of the User class by calling the constructor with the specified values for name, age, weight, address, and gender.

Displaying User Information:

console.log(user.printUser());

This line calls the printUser method on the user instance, which generates a string containing the user’s information and logs it to the console.

Output:

User: { name: Abhishek, age: 22, weight: 55, address: India, gender: Male }

Before we move to implementing Builder Method we have to analyze what is wrong with this and what issues are solved by implementing builder method, at first we see the above code we realized that this is a correct and easy way to create a new object but we have to provide all information during initialization. If we look closely at the line:

const user = new User(‘Abhishek’ , 22 , 55 , ‘India’ , ‘Male’ );

we see that properties of this user object can be confusing, like sometime we can mistakenly give age instead of weight and weight instead of age . As our code size grows, we will have to look at the class to figure out which properties we have to provide when initializing a user object.

For all these problems we have a design solution called Builder Method.

Implementation of the above Example using Builder Design Pattern

Implementation user Class:

Javascript

//Blueprint for creating a new user using User class

class User {
  constructor(name) {
    this.name = name;
    this.age = null;
    this.weight = null;
    this.address = null;
    this.gender = null;
  }

  // Method to set Age of the user
  setAge(age) {
      this.age = age;
      return this;   // Return the object for method chaining
    }

  // Method to set the Weight of the user
  setWeight(weight) {
    this.weight = weight;
    return this;    // Return the object for method chaining
  }

  // Method to set the Address of the user
  setAddress(address) {
    this.address = address;
    return this;   // Return the object for method chaining
  }
  // Method to set the gender of user
  setGender(gender) {
    this.gender = gender;
    return this;    // Return the object for method chaining
  }

  //Method to finalize the user creation
  build() {
    if (!this.name) {
      throw Error('Name is required');
    }
    return this;   // Return the object for method chaining
  }

  printUser() {
    return `User: { name: ${this.name}, age: ${this.age}, weight: ${this.weight}, address: ${this.address}, gender: ${this.gender} }`;
  }
}
// Usage
const user = new User('Abhishek').setAge(30).setGender('Male').build();

console.log(user.printUser());

Note: In build method, we have only checked for name but we can also add more checks

Explanation of the above example using Builder Design Pattern:

User Class Definition:

Javascript

class User {
  constructor(name) {
    this.name = name;
    this.age = null;
    this.weight = null;
    this.address = null;
    this.gender = null;
  }
}

Here, a User class is defined with a constructor that takes a name parameter and initializes other user attributes (age, weight, address, gender) to null.

Setting User Attributes:

Javascript

setAge(age) {
  this.age = age;
  return this;
}
setWeight(weight) {
  this.weight = weight;
  return this;
}
setAddress(address) {
  this.address = address;
  return this;
}
setGender(gender) {
  this.gender = gender;
  return this;
}

These set methods allow you to set the user’s age, weight, address, and gender. They update the corresponding attributes and return the object to enable method chaining.

Finalizing User Creation:

Javascript

build() {
  if (!this.name) {
    throw Error('Name is required');
  }return this;     // Return the object for method chaining
}

The build method is used to finalize user creation. It checks if the name is provided and throws an error if it’s not. It returns the object to allow method chaining.

Printing User Information:

Javascript

printUser() {
  return `User: { name: ${this.name}, age: ${this.age}, weight: ${this.weight}, address: ${this.address}, gender: ${this.gender} }`;
}

The printUser method generates a string representation of the user’s information.

Usage:

Javascript

const user = new User('Abhishek').setAge(30).setGender('Male').build();
console.log(user.printUser());

This creates a new user with the name “Abhishek”, sets the age to 30, and sets the gender to “Male”. Then the build method is called to finalize user creation. Finally, the printUser method is used to print the user’s information to the console.

Output:

User: { name: Abhishek, age: 30, weight: null, address: null, gender: Male }

Implementation using Function:

Javascript

// Factory function to create a user object

function createUser(name) {

  const user = {
    name,
    age: null,
    weight: null,
    address: null,
    gender: null,

    // Method to set the age of the user
    setAge(age) {
      this.age = age;
      return this;     // Return the object for method chaining
    },

    // Method to set the weight of the user
    setWeight(weight) {
      this.weight = weight;
      return this;     // Return the object for method chaining
    },

    // Method to set the address of the user
    setAddress(address) {
      this.address = address;
      return this;    // Return the object for method chaining
    },

    // Method to set the gender of the user
    setGender(gender) {
      this.gender = gender;
      return this;   // Return the object for method chaining
    },

    // Method to finalize the user creation
    build() {
      if (!this.name) {
        throw Error('Name is required'); // Validate required properties
      }
      return this;   // Return the object for method chaining
    },

    // Method to display the user information as a string
    printUser() {
      return `User: { name: ${this.name}, age: ${this.age}, weight: ${this.weight}, address: ${this.address}, gender: ${this.gender} }`;
    }
  };

  return user;     // Return the user object
}

// Usage: Create a user object and set properties
const user = createUser('Abhishek')
  .setAge(30)
  .setWeight(70)
  .setAddress('India')
  .setGender('Male')
  .build();       // Finalize user creation

console.log(user.printUser());     // Display user information

Below is the explanation of the above code:

Factory Function to Create User Object:

Javascript

function createUser(name) {
  const user = { ... };  // Object with user properties and methods
  return user;       // Return the user object
}

Here, a factory function createUser is used to create and initialize objects. The function takes a name parameter and returns a user object with properties and functions .

Setting User Attributes:

Javascript

setAge(age) {
  this.age = age;
  return this;
}
setWeight(weight) {
  this.weight = weight;
  return this;
}
setAddress(address) {
  this.address = address;
  return this;
}
setGender(gender) {
  this.gender = gender;
  return this;
}

These sets functions allow you to set the user’s age, weight, address, and gender. They update the corresponding attributes and return the object to enable function chaining.

Finalizing User Creation:

Javascript

build() {
  if (!this.name) {
    throw Error('Name is required');
  }return this;               // Return the object for method chaining
}

The build functions is used to finalize user creation. It checks if the name is provided and throws an error if it’s not. It returns the object to allow function chaining.

Printing User Information:

Javascript

printUser() {
  return `User: { name: ${this.name}, age: ${this.age}, weight: ${this.weight}, address: ${this.address}, gender: ${this.gender} }`;
}

The printUser function generates a string representation of the user’s information.

Usage:

Javascript

const user = new User('Abhishek').setAge(30).setGender('Male').build();
console.log(user.printUser());

• This creates a new user with the name “Abhishek”, sets the age to 30, sets the gender to “Male”, sets the address to India and weight to 70.
• Then build function is called to finalize user creation.
• Finally, the printUser function is used to print the user’s information to the console.

Output:

Javascript

User: { name: Abhishek, age: 30, weight: 70, address: India, gender: Male }

Advantages of the Builder Design Pattern:

• Improved Object Creation: The Builder pattern allows for the step-by-step construction of an object, making the creation process more understandable and manageable.
• Flexible Object Construction: It provides flexibility by allowing different configurations for constructing objects.
• Code Readability: The code using the Builder pattern is often more readable and self-explanatory, as method names in the builder convey the intention of the construction steps.

Disadvantages of the Builder Design Pattern:

• Code Overhead: Implementing the Builder pattern requires creating a separate builder class or methods, which can introduce additional code and complexity.
• Not Suitable for Simple Objects: For simple objects that do not have a significant number of properties or configurations, the Builder pattern may be overly complex.

Where to Use the Builder Design Pattern:

• Complex Object Creation: Use the Builder pattern when dealing with complex objects that require multiple configurations and parameters for creation.
• Object Initialization Flexibility: When you want to provide flexibility in the order of setting properties and handle optional parameters.

Where Not to Use the Builder Design Pattern:

Simple Objects: For objects with a small number of properties or minimal configuration requirements, the Builder pattern might introduce unnecessary complexity.