throttle

Throttle: when a function is triggered rapidly, run it at most once per interval. The first call runs immediately (leading edge) and the last call inside a window is replayed when the window closes (trailing edge), so the final state is never dropped.

Use it for scroll, pointer-move and drag: anything that needs continuous feedback. For "only the final value matters" (search-as-you-type, autosave), use debounce.

API

throttle(fn, delay?)

Parameters

Parameter	Description	Type	Default
`fn`	Function to throttle	`Function`	Required
`delay`	Minimum interval (ms)	`number`	`300`

Return

A throttled function that keeps the call-site this and arguments, plus:

Member	Description	Type
`cancel()`	Drop the pending trailing call	`() => void`
`pending()`	Whether a trailing call is waiting	`() => boolean`

Example

import { throttle } from 'ranuts';

const onScroll = throttle(() => update(window.scrollY), 100);
window.addEventListener('scroll', onScroll);

// On teardown — remove the listener *and* drop the pending trailing call
window.removeEventListener('scroll', onScroll);
onScroll.cancel();

Notes

Leading + trailing: runs immediately, then once more at the end of the window with the latest arguments.
this and arguments are forwarded from the call site.
Runs anywhere: uses the bare setTimeout, so it works in Node, Web Workers and SSR.
Each call to throttle() gets its own window — two throttled functions never interfere.
Always cancel() on teardown, otherwise the trailing call fires into a destroyed context.