Typescript debounce function not calling function passed as parameter

This is intended as a supplement to Saveli Tomac's excellent answer.

In the comments I said I didn't think that implementation was particularly good. In particular it has two problems:

1. It doesn't have an immediate option. Most debounce implementations in the wild (including the one you linked in your question) have this.
2. The returned function ignores the this value.

Here's an example that fixes these:

const debounce = (n: number, fn: (...params: any[]) => any, immed: boolean = false) => {
  let timer: number | undefined = undefined;
  return function (this: any, ...args: any[]) {
    if (timer === undefined && immed) {
      fn.apply(this, args);
    }
    clearTimeout(timer);
    timer = setTimeout(() => fn.apply(this, args), n);
    return timer;
  }
};

Typescript Playground

How do you use your debounce function? I prepare fiddle, you can check working solution here

function debounce<Params extends any[]>(
  func: (...args: Params) => any,
  timeout: number,
): (...args: Params) => void {
  let timer: NodeJS.Timeout
  return (...args: Params) => {
    clearTimeout(timer)
    timer = setTimeout(() => {
      func(...args)
    }, timeout)
  }
}

function test(message) {
  alert(message);
}

const debouncedTest = debounce(test, 2000);

debouncedTest('message');

Well, it's not typescript troubles