What Is DaloyJS? A Beginner-Friendly Tour of a Contract-First TypeScript Framework

Devlin Duldulao Posted on May 30 What Is DaloyJS? A Beginner-Friendly Tour of a Contract-First TypeScript Framework # webdev # typescript # node # beginners When I started building APIs, I spent way too much of my life keeping three things in sync: the actual route code, the validation, and the docs. You change one field, you forget the other two, and a week later someone on the frontend team pings you asking why the docs say title but the API returns name . Been there. Shipped that bug. Apologized in standup. DaloyJS is the framework I wish I had back then. Let me walk you through what it is, in plain language, without assuming you have ten years of backend scars. The one-sentence version DaloyJS is a TypeScript web framework where you define a route once, and from that single definition you get validation, types, OpenAPI docs, and a typed client SDK. No copy-pasting. No drifting docs. If you have heard of FastAPI in the Python world, that "write it once, get docs for free" feeling is exactly what DaloyJS brings to TypeScript. Why should a junior developer care? Here is the thing nobody tells you early on: most of the pain in backend work is not writing the logic. It is keeping everything that describes your logic honest. The docs, the input validation, the response shapes, the client code. They all want to lie to you the moment you stop watching them. DaloyJS makes one definition the single source of truth. You write a route, and that route is the contract. That is what "contract-first" means. The framework reads your contract and generates the boring stuff for you. What a route looks like Here is a real example. Do not worry about understanding every line yet, just look at the shape of it. import { App , NotFoundError } from " @daloyjs/core " ; import { z } from " zod " ; const BookSchema = z . object ({ id : z . string (), title : z . string () }); const app = new App ({ openapi : { info : { title : " Bookstore API " , version : " 1.0.0 " } }, docs : true , });