Simple JavaScript Debounce Function

new_gist_file.js

// Returns a function, that, as long as it continues to be invoked, will not
// be triggered. The function will be called after it stops being called for
// N milliseconds. If `immediate` is passed, trigger the function on the
// leading edge, instead of the trailing.
function debounce(func, wait, immediate) {
	var timeout;
	return function() {
		var context = this, args = arguments;
		clearTimeout(timeout);
		timeout = setTimeout(function() {
			timeout = null;
			if (!immediate) func.apply(context, args);
		}, wait);
		if (immediate && !timeout) func.apply(context, args);
	};
}


/* minified */
function debounce(a,b,c){var d;return function(){var e=this,f=arguments;clearTimeout(d),d=setTimeout(function(){d=null,c||a.apply(e,f)},b),c&&!d&&a.apply(e,f)}}

/* usage */

var myEfficientFn = debounce(function() {
	// All the taxing stuff you do
}, 250);

window.addEventListener('resize', myEfficientFn);

If we write this in TS? what would be the type of callback and ...args

interface DebouncedFunction {
  (): any;
  cancel: () => void;
}

export const debounce = <F extends (...args: any[]) => ReturnType<F>>(
  func: F,
  wait: number,
  immediate?: boolean
) => {
  let timeout: number = 0;

  const debounced: DebouncedFunction = function(this: void) {
    const context: any = this;
    const args = arguments;

    const later = function() {
      timeout = 0;
      if (!immediate) func.call(context, ...args);
    };
    const callNow = immediate && !timeout;
    clearTimeout(timeout);
    timeout = window.setTimeout(later, wait);
    if (callNow) func.call(context, ...args);
  };

  debounced.cancel = function() {
    clearTimeout(timeout);
    timeout = 0;
  };

  return debounced as (...args: Parameters<F>) => ReturnType<F>;
};

If found that, when setting immediate to true the debounced function was not invoked at all.
This is because as soon as you get at if (immediate && !timeout) the timeout variable was just set.
Maybe move that if statement to before setting timeout?

This 👆

My TypeScript solution:

function debounce(func: (...args: unknown[]) => unknown, delay = 200) {
  let timeout: number;

  return function (...args: unknown[]) {
    clearTimeout(timeout);
    timeout = setTimeout(() => func(...args), delay);
  };
}

or maybe (also when running in node or web)

function debounce<T>(func: (...args: T[]) => unknown, delay = 200) {
  let timeout: number | NodeJS.Timeout;

  return function (...args: T[]) {
    clearTimeout(timeout as number);
    timeout = setTimeout(() => func(...args), delay);
  };
}

I suggest adding to our debounce function return type unknown or I prefer typeof func as shown on line 4 below:

function debounce<T>(
  func: (...args: T[]) => unknown,
  delay = 200
): typeof func {
  let timeout: number | NodeJS.Timeout;
  return function (...args: T[]) {
    clearTimeout(timeout as number);
    timeout = setTimeout(() => func(...args), delay);
  };
}

Without it results may be faced with type conversion issues a la ts(2352).

As indicated above, in the main gist function, using immediate will break the implementation
So, for such needs where we wanted to call the function immediately (leading edge instead of trailing)
Try this implementation https://youmightnotneed.com/lodash#function