Problem: Build a Minimal Email Template Builder

Easy

15 min

Implement a fluent builder to construct basic email templates.

Problem statement

Your team needs a flexible way to construct transactional emails, such as welcome messages, password resets, and usage alerts. Right now, it’s all handled with fragile object literals and scattered logic. You’re refactoring toward a more expressive API that reads like a recipe.

Goal

Create an EmailBuilder class with the following chainable methods:

.to(email: string)
.withSubject(subject: string)
.withBody(content: string)
.build(): Returns the final object with shape :{ to, subject, body }

All fields are required before calling .build(). If any field is missing, throw an error.

Constraints

Do not use constructor parameters to initialize the email.
Do not allow optional chaining or fallback defaults inside .build().
Use method chaining to construct the object—no helper function wrappers.

Sample output

The examples below illustrate what the output should look like:

// Happy path
const email1 = new EmailBuilder()
  .to('user1@example.com')
  .withSubject('Welcome!')
  .withBody('Glad you’re here.')
  .build();
console.log(email1);
/* Expected output:
{ to: 'user1@example.com',
  subject: 'Welcome!',
  body: 'Glad you’re here.' } */
// Missing subject
try {
  const email2 = new EmailBuilder()
    .to('user2@example.com')
    .withBody('No subject line.')
    .build();
} catch (err) {
  console.log('Failed to build email2:', err.message);
}
/* Expected output:
Failed to build email2: Missing required email fields */
// Another valid email (out-of-order chaining)
const email3 = new EmailBuilder()
  .withBody('Don’t forget our meeting.')
  .withSubject('Reminder')
  .to('user3@example.com')
  .build();
console.log(email3);
/* Expected output:
{ to: 'user3@example.com',
  subject: 'Reminder',
  body: 'Don’t forget our meeting.' } */
// Missing recipient
try {
  const email4 = new EmailBuilder()
    .withSubject('No recipient')
    .withBody('We need someone to send this to.')
    .build();
} catch (err) {
  console.log('Failed to build email4:', err.message);
}
/* Expected output:
Failed to build email4: Missing required email fields */

Problem: Build a Minimal Email Template Builder

Easy

15 min

Implement a fluent builder to construct basic email templates.

Problem statement

Goal

Create an EmailBuilder class with the following chainable methods:

.to(email: string)
.withSubject(subject: string)
.withBody(content: string)
.build(): Returns the final object with shape :{ to, subject, body }

All fields are required before calling .build(). If any field is missing, throw an error.

Constraints

Do not use constructor parameters to initialize the email.
Do not allow optional chaining or fallback defaults inside .build().
Use method chaining to construct the object—no helper function wrappers.

Sample output

The examples below illustrate what the output should look like:

// Happy path
const email1 = new EmailBuilder()
  .to('user1@example.com')
  .withSubject('Welcome!')
  .withBody('Glad you’re here.')
  .build();
console.log(email1);
/* Expected output:
{ to: 'user1@example.com',
  subject: 'Welcome!',
  body: 'Glad you’re here.' } */
// Missing subject
try {
  const email2 = new EmailBuilder()
    .to('user2@example.com')
    .withBody('No subject line.')
    .build();
} catch (err) {
  console.log('Failed to build email2:', err.message);
}
/* Expected output:
Failed to build email2: Missing required email fields */
// Another valid email (out-of-order chaining)
const email3 = new EmailBuilder()
  .withBody('Don’t forget our meeting.')
  .withSubject('Reminder')
  .to('user3@example.com')
  .build();
console.log(email3);
/* Expected output:
{ to: 'user3@example.com',
  subject: 'Reminder',
  body: 'Don’t forget our meeting.' } */
// Missing recipient
try {
  const email4 = new EmailBuilder()
    .withSubject('No recipient')
    .withBody('We need someone to send this to.')
    .build();
} catch (err) {
  console.log('Failed to build email4:', err.message);
}
/* Expected output:
Failed to build email4: Missing required email fields */

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Node.js

class EmailBuilder {
  // implement methods here
}
// Example usage:
// Happy path
const email1 = new EmailBuilder()
  .to('user1@example.com')
  .withSubject('Welcome!')
  .withBody('Glad you’re here.')
  .build();
console.log(email1);
/* Expected output:
{ to: 'user1@example.com',
  subject: 'Welcome!',
  body: 'Glad you’re here.' } */
// Missing subject
try {
  const email2 = new EmailBuilder()
    .to('user2@example.com')
    .withBody('No subject line.')
    .build();
} catch (err) {
  console.log('Failed to build email2:', err.message);
}
/* Expected output:
Failed to build email2: Missing required email fields */
// Another valid email (out-of-order chaining)
const email3 = new EmailBuilder()
  .withBody('Don’t forget our meeting.')
  .withSubject('Reminder')
  .to('user3@example.com')
  .build();
console.log(email3);
/* Expected output:
{ to: 'user3@example.com',
  subject: 'Reminder',
  body: 'Don’t forget our meeting.' } */
// Missing recipient
try {
  const email4 = new EmailBuilder()
    .withSubject('No recipient')
    .withBody('We need someone to send this to.')
    .build();
} catch (err) {
  console.log('Failed to build email4:', err.message);
}
/* Expected output:
Failed to build email4: Missing required email fields */