One of the biggest misconceptions I had early in my career was believing JavaScript itself handled things like:

timers

network requests

DOM events

file system operations

It turns out…

JavaScript engines like V8 don’t actually implement any of those features.

Take this example:

```js id="g7q2vn"

setTimeout(() => {

console.log("Hello");

}, 2000);

Most developers assume:

> JavaScript starts a timer and waits 2 seconds.

But that’s not what happens.

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# What V8 Actually Does

V8 only handles:

* parsing JavaScript * compiling JavaScript * executing JavaScript

That’s it.

It has no built-in understanding of:

* timers * HTTP requests * mouse clicks * file systems * sockets

Those capabilities are provided by the runtime environment around V8.

Depending on where your code runs, that runtime could be:

* the browser * Node.js * Deno * Bun

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# So who handles `setTimeout()`?

When you call:

```js id="dx9s1f" setTimeout(fn, 2000);

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the flow looks…