Debounce vs Throttle with examples

Author: Daniel Einars

Date Published: 01.11.2022

1. Overview

Every single time I'm calling a function a lot of times in quick succession I ask myself

Wait... should I debounce call or throttle this call?

So for the sake of preserving my sanity (and maybe yours), I'll briefly explain what each function does and when to use which.

2. Debounce

This function essentially cancels running calls until it hasn't been called for a set period of time. This makes it ideal for making sure that search query is only sent to the endpoint once the user is finished typing the query.

function debounce(callback, delay = 500){
  let timeoutId;
  function debounced(...args){
    if(timeoutId){
      clearTimeout(timeoutId)
    }
    timeoutId = setTimeout(() => {
      callback(...args)
    }, delay)
  }
  return debounced
}

3. Throttle

Throttling a function call will reduce the number of times that function is called. It does that by setting a timeout and only calling the last function once the timeout is complete. An implementation of throttle could look something like this

function throttle(callback, delay = 500) {
  var wait = false;

  function throttled(...args) {
    if (!wait) {
      callback(...args);
      wait = true;
      setTimeout(function () {
        wait = false;
      }, delay);
    }
  }
  
  return throttled
}

This snippet will cancel all calls which happen within the delay. Sometimes you'll want to que the last call.


function throttle(callback, delay = 500) {
  let shouldWait = false
  let quedArguments

  function quedCallback() {
    if (quedArguments == null) {
      shouldWait = false
    } else {
      callback(...quedArguments)
      quedArguments = null
      setTimeout(quedCallback, delay)
    }
  }


  function throttled(...args) {
    if (shouldWait) {
      quedArguments = args
      return
    }

    shouldWait = true
    setTimeout(quedCallback, delay)
  }

  return throttled
}

The major difference here is that we're saving the ...args in the quedArguments variable and calling the callback with the last quedArguments contents.