How to Build a Frontend Framework to Learn React Internals

Why should a self-taught developer build a framework from scratch?

Most self-taught developers learn React or Vue by tutorial and muscle memory, but never see what happens beneath `useState` or the reactivity system. This methodology's core principle is no black boxes: if you cannot create it, you do not understand it. By hand-building templating, a virtual DOM, and state management, you turn framework 'magic' into mechanics you can explain in an interview or debug in production.

You don't reinvent everything — you use Snabbdom (the same virtual DOM library Vue forked) for diffing and patching, so you can focus on the design decisions that actually teach you how frameworks think.

What will you actually build first?

Start small. Build a Profile Card component: `initialState = { name: 'Alex', jobTitle: 'Engineer' }`, a mutation `changeTitle: (state, newTitle) => ({ ...state, jobTitle: newTitle })`, and a template that renders the name and title with an `onClick` handler. Pass all three — template, methods, initial state — to `createComponent`.

When you click the button, the mapped method automatically updates state, re-evaluates the template, and patches only the changed text node. That single interaction demonstrates reactivity, pure state transformation, and scoped DOM updates all at once.

Then build a counter widget with `increment` and `decrement` mutations to cement how Snabbdom patches only the count text node while leaving the rest untouched.

How does this make you a better React or Vue developer?

Once you've hand-built mapped methods, React's `setState` and Vue's reactive proxies stop feeling mysterious — you've written the equivalent yourself. You'll instinctively understand why you never mutate state in place (it breaks change detection), why declarative templates re-render from state, and why virtual DOM diffing is more efficient than manual DOM manipulation.

This is exactly the depth that separates developers who use frameworks from developers who understand them. It also directly maps to common interview questions about reconciliation, the virtual DOM, and immutability.

What should you learn before starting?

The creator explicitly warns that without solid JavaScript fundamentals, the codebase becomes opaque. Make sure you're comfortable with:

- Tagged template literals — the template engine core

- The spread operator — how state mutations return new objects

- Destructuring — used throughout component definitions

- `reduce` — the mechanism inside `createElement` and `createReducer`

If any of these feel shaky, spend a weekend on them first. They're the foundation every part of the framework rests on.

What's the recommended build order?

1. Scaffold with Parcel (zero config) and install Snabbdom via yarn.

2. Build `createElement(tagName)` as a higher-order function using tagged template literals.

3. Refactor it to output Snabbdom virtual nodes via the `h` function, extracting a `createReducer` helper.

4. Build the `init` function to patch the real DOM once.

5. Add event handling with Snabbdom's eventlisteners module and `onClick` factories.

6. Define initial state and pure mutation functions.

7. Implement `createComponent` with mapped methods for reactivity.

8. Author your Profile Card, wire it into `index.js`, and run `yarn start`.

Follow this layered order strictly — skipping the `createReducer` refactor, for example, makes adding events painful later.

Next step: Clone a fresh Parcel project tonight and build the counter widget end to end. Once it patches only the count node on click, you'll have proven to yourself that you understand reactivity — no black boxes.