debounce.ts

import type { λ } from "./types.ts";

export const cancel = Symbol("debounce.cancel");

/**
 * Creates a debounced function that delays invoking `fun` until `ms` milliseconds
 * have passed since the last invocation of the debounced function.
 *
 * `fun` is invoked with the last arguments passed to the debounced function.
 *
 * Calling `[debounce.cancel]()` on the debounced function will cancel the currently
 * scheduled invocation.
 */
const debounce = Object.assign(
  (fun: λ, ms: number) => {
    let toId: any;
    return Object.assign(
      (...args: any[]) => {
        clearTimeout(toId);
        toId = setTimeout(() => fun(...args), ms);
      },
      { [cancel]: () => clearTimeout(toId) },
    ) as any;
  },
  { cancel },
) as
  & (<T extends λ>(
    fun: T,
    ms: number,
  ) => λ<Parameters<T>, void> & { [cancel](): void })
  & {
    cancel: typeof cancel;
  };

export default debounce;