Most developers write this code every day: ```js id="e9u2xa" setTimeout(() => { console.log("Hello"); }, 2000); and assume JavaScript is responsible for the timer. But that’s not actually true. ## The surprising reality JavaScript engines like V8 do **not** have built-in timer functionality. V8 only knows how to: * parse JavaScript * compile JavaScript * execute JavaScript That’s it. Functions like: * `setTimeout()` * `fetch()` * `addEventListener()` * `console.log()` are **not provided by JavaScript itself**. They come from the runtime environment: * Browsers * Node.js * Native system libraries --- # What happens when `setTimeout()` runs? When you execute: ```js id="n5lf4v" setTimeout(callback, 2000); Enter fullscreen mode Exit fullscreen mode the flow is roughly: ```text id="38dxux" JavaScript ↓ V8 Engine ↓ Runtime Bindings ↓ Native C/C++ APIs ↓ Operating System The runtime delegates the timer to native code.…