Wait for the next event loop

Resolve after the current task, letting queued timers, I/O and rendering run.

JavaScriptNode.js & browsers Version 1.0.0 · MIT · .md

function nextTask() { return new Promise(resolve => setTimeout(resolve, 0)); }

Usage

const order = [];
const done = nextTask().then(() => order.push('timer'));
Promise.resolve().then(() => order.push('microtask'));
order.push('sync');
await done;
order; // → ['sync', 'microtask', 'timer']

Lines marked → were executed in Node.js 22 and in headless Chromium, and each result was compared with the value shown. Lines marked e.g. are illustrative.

Know the limits

• Promise callbacks (microtasks) still run before the timer, as the example shows.
• The HTML standard clamps timers nested more than five levels deep to at least 4 ms, so a chain of zero-delay timers is slower than it looks.
• In Node.js, setImmediate runs after pending I/O callbacks.

The function above is the code the usage lines run. It does not validate its arguments; add checks where it receives untrusted input.

Keep exploring

• Convert Celsius to Fahrenheit — Apply the temperature conversion without rounding the result.
• Convert hex to RGB — Expand #rgb if needed and read the red, green and blue channels.
• Convert URL parameters to object — Read a query string into an object; repeated keys become arrays.