Type-safe Template Generator Design in TypeScript

Описание: Learn how to build a type-safe, scalable document generator in TypeScript that selects templates with strongly-typed parameters for clean, maintainable code.
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This video is based on the question https://stackoverflow.com/q/79348809/ asked by the user 'cuaies' ( https://stackoverflow.com/u/19272566/ ) and on the answer https://stackoverflow.com/a/79348956/ provided by the user 'Matt Timmermans' ( https://stackoverflow.com/u/5483526/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Introduction

When building a document generator service supporting multiple templates (e.g., invoices, reports), each with distinct data and layout, it’s crucial to maintain type safety and scalability. The goal is for a centralized method to accept a template identifier and generate documents with the correct, type-checked parameters — all while keeping the service stateless.

Problem Statement

Multiple document templates require different parameter types.

A DocumentGenerator.create() method should accept:

A template enum value (e.g., TemplateEnum.Invoice, TemplateEnum.Report).

Template-specific, type-checked data matching the selected template.

The design should remain stateless and extensible for future template additions.

Solution Overview

Use TypeScript’s mapped types and generics to:

Define an interface that maps each template enum to its corresponding parameter type.

Use generics in the create() method to infer the correct parameter type based on the template selected.

Ensure compile-time type safety so invalid data-template combinations are caught early.

Step-by-Step Implementation

1. Define Templates and Data Types

[[See Video to Reveal this Text or Code Snippet]]

2. Map Templates to Generator Functions

Define a mapping interface connecting template enum values to generator function signatures:

[[See Video to Reveal this Text or Code Snippet]]

3. Implement the DocumentGenerator Class

Use a generic method to infer parameter types based on the template:

[[See Video to Reveal this Text or Code Snippet]]

4. Usage Example

[[See Video to Reveal this Text or Code Snippet]]

Benefits of This Approach

Type safety: Incorrect data-template mismatches are caught at compile time.

Scalability: Add new templates by extending enum, data interfaces, and generator map.

Statelessness: Generator functions are pure and depend only on input data.

Maintainability: Centralized and clean method create() abstracts generation details.

Conclusion

Leveraging TypeScript’s powerful type system for mapping templates to their data types allows building a clean, flexible, and type-safe document generator. This pattern ensures your code remains robust and scalable as your document types grow.