Code Your Own Virtual DOM in 100 Lines of JavaScript

Code Your Own Virtual DOM in 100 Lines of JavaScript Introduction: Open the Black Box You've been using React for years. You know how to lift state, split components, and reach for useMemo when things get slow. But ask yourself: what does React's render() actually do? Most developers never look. The framework works, so they don't have to. That's fine — until they hit a bug they can't explain, a performance profile that makes no sense, or a mental model with a hole in it the size of a reconciliation algorithm. Here's the thing that most introductions get wrong: the Virtual DOM is not a performance optimization. Rich Harris, creator of Svelte, made this argument in 2018 and it still holds. A VDOM doesn't make DOM operations faster — it adds a layer of work on top of them. What it gives you is something more valuable: a programming model where you describe what the UI should look like, not how to get there. The framework figures out the minimal set of changes. You just write the output. T