flush

Synchronously processes the pending reactive queue, or runs fn in a synchronous flush scope before draining the queue.

Reactive updates are normally batched onto the microtask queue, so multiple writes in a row collapse into a single update pass. Call flush() when you need to observe the result of those writes synchronously — most commonly in tests, but also at the boundary of imperative integration code. Pass a callback when the writes themselves should bypass microtask scheduling and drain synchronously when the callback returns.

Import

import { flush } from "solid-js";

Type signature

function flush(): void;
function flush<T>(fn: () => T): T;

Examples

const [count, setCount] = createSignal(0);
const doubled = createMemo(() => count() * 2);

setCount(5);
flush();
expect(doubled()).toBe(10);

flush(() => setCount(6));
expect(doubled()).toBe(12);

// Nested flushes drain at each level:
flush(() => {
  setCount(7);
  flush(() => setCount(8)); // inner drain — effects fire here
  // outer continues with up-to-date state
});