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Creating a progress bar...

Black Ducas test
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Go to solution Solved by mvaneijgen,

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10 hours ago, GSAP Helper said:

Without a minimal demo, it's very difficult to troubleshoot; the issue could be caused by CSS, markup, a third party library, a 3rd party script, etc. Would you please provide a very simple CodePen or Stackblitz that illustrates the issue? 


Please don't include your whole project. Just some colored <div> elements and the GSAP code is best. See if you can recreate the issue with as few dependancies as possible. Start minimal and then incrementally add code bit by bit until it breaks. Usually people solve their own issues during this process! If not, at least we have a reduced test case which greatly increases your chances of getting a relevant answer.



Here it is


The error I said is on the Codepen too:




Orignal topic 



Hi, I'm trying the quoted code.

function progressBarUpdate(tween) {

const tl = gsap.timeline({
  delay: 1,
  onUpdate: progressBarUpdate,
  .add(reveal(), 'reveal')


The timeline itself works perfectly. I just added onUpdate: progressBarUpdate and the function, and I get this error:


Uncaught TypeError: Cannot read properties of undefined (reading 'progress')
    at Timeline.progressBarUpdate [as _onUpdate]

The problem comes from this line console.log(tween.progress())


Any idea?


See the Pen dyrqqPy?editors=1111 by gooogooo (@gooogooo) on CodePen

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Hi @Black Ducas I've split your reply to its own topic, no need to bother all these people 9 years later. 


If you would have logged tween you would see that you don't have access to it, because you never pass it to the function that you call in onComplete


If you pass the current timeline as an argument to the function, you do have access to it. Check out how functions work in Javascript https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Functions Hope it helps and happy tweening! 


See the Pen oNVPPxN?editors=0011 by mvaneijgen (@mvaneijgen) on CodePen

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  • Solution

Yeah probably something has changed 9 years later, no worries. It is always a good idea to log the things you get to make sure they are what you think they are. 


In this case you can do two things. You want to tween a timeline, so all the logic should move to the timeline. Pausing a tween and then controlling the timeline is what is tripping you up here. 

// With a timeline 
let progressBarTl = gsap.timeline({
    paused: true, // Timeline gets paused
progressBarTl.from(".progress-bar", {
  scaleX: 0,
  duration: 2,
  ease: "none"

// Using a single tween
const progressBarTl = gsap.from(".progress-bar", {
  paused: true, // Tween gets paused
  scaleX: 0,
  duration: 2,
  ease: "none"

See the Pen QWoVZEP?editors=0010 by mvaneijgen (@mvaneijgen) on CodePen


Hope it helps and happy tweening! 

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