Type Safe Builder Pattern

A lightweight, zero-dependency TypeScript implementation of the Builder Design Pattern. This package ensures total type safety by preventing you from calling .build() until all required properties of your schema are defined.

✨ Key Features

• 🔒 Type Completion Enforcement: The .build() method is hidden via TypeScript's type system until every required property is set.
• 🧊 Immutable by Design: Every .set() call returns a new instance of the builder, allowing for easy branching and state sharing without side effects.
• 🛠️ Complex Type Support: Seamlessly handles Optionals, Unions, Enums, Nested Objects, Arrays, and Template Literals.
• 🚀 Bun Optimized: Developed and tested using the Bun runtime for maximum performance.

📦 Installation

# Using npm
npm install type-safe-builder-pattern

# Using bun
bun add type-safe-builder-pattern

🚀 Quick Start

The core power of this library is that it makes "incomplete" objects impossible to build.

import { objectBuilder } from "type-safe-builder-pattern";

type User = {
    id: number;
    username: string;
    email: string;
    isAdmin?: boolean; // Optional
};

const builder = objectBuilder<User>()
    .set("id", 1)
    .set("username", "romeosarkar");

// ERROR: .build() does not exist yet because 'email' is missing!
// builder.build();

const user = builder.set("email", "[email protected]").build(); // Now it works!

console.log(user);
// { id: 1, username: "romeosarkar", email: "[email protected]" }

💡 Advanced Usage

🌿 Immutability & Branching

Since each .set() returns a new instance, you can create a base configuration and branch off it.

const baseConfig = objectBuilder<Config>()
    .set("host", "localhost")
    .set("port", 5432);

const devConfig = baseConfig.set("database", "dev_db").build();
const prodConfig = baseConfig.set("database", "prod_db").build();

🧩 Nested Objects & Arrays

The builder maintains full type safety for complex nested structures.

type Project = {
    name: string;
    tags: string[];
    metadata: {
        version: string;
    };
};

const myProject = objectBuilder<Project>()
    .set("name", "TypeSafeApp")
    .set("tags", ["typescript", "builder"])
    .set("metadata", { version: "1.0.0" })
    .build();

🛠️ Development

This project uses Bun for development and testing.

Prerequisites

• Bun >= 1.x
• Node.js >= 25 (for runtime compatibility)

Setup

# Install dependencies
bun install

# Run tests
bun test

# Build the project
bun run build

# Format code
bun run format

📄 License

MIT © Romeo Sarkar

Why use this instead of a plain object?

In large-scale applications, creating complex objects with many required fields can become messy. Using this builder:

1. Prevents Runtime Errors: You can't accidentally forget a field.
2. Improves Readability: Named .set(key, value) calls are often clearer than large object literals.
3. Encourages Immutability: Easier to maintain state in functional environments.