Optimizer

Qwik's philosophy is to delay loading code for as long as possible. To do that, Qwik relies on Optimizer to re-arrange the code for lazy loading. The Optimizer is code level transformation that runs as part of the rollup. (Optimizer is written in Rust (and available as WASM) for instant performance)

The Optimizer looks for $ and applies a transformation that extracts the expression following the $ and turns it into a lazy-loadable and importable symbol.

Let's start by looking at a simple Counter example:

export const Counter = component$(() => {
  const count = useSignal(0);
 
  return <button onClick$={() => count.value++}>{count.value}</button>;
});

The above code represents what a developer would write to describe the component. Below are the transformations that the Optimizer applies to the code to make the code lazy-loadable.

const Counter = component(qrl('./chunk-a.js', 'Counter_onMount'));

export const Counter_onMount = () => {
  const count = useSignal(0);
  return <button onClick$={qrl('./chunk-b.js', 'Counter_onClick', [count])}>{count.value}</button>;
};

const Counter_onClick = () => {
  const [count] = useLexicalScope();
  return count.value++;
};

Notice that every occurrence of $ results in a new lazy loadable symbol.

Serialization

See serialization for a discussion of what is serializable.