By Maria Antonietta Perna

GreenSock for Beginners: a Web Animation Tutorial (Part 1)

By Maria Antonietta Perna

Beyond CSS: Dynamic DOM Animation Libraries

Animating the DOM with GreenSock (GSAP)

My aim in this article is to give you a thorough introduction to GreenSock, also known as GSAP (GreenSock Animation Platform), a super performant, professional-grade HTML5 animation engine for the modern web.

This is the fourth article in the series Beyond CSS: Dynamic DOM Animation Libraries.

Here’s what I covered in the past issues:

GSAP has too many features to fit in one article. This is why I’ve opted for a multi-part article all dedicated to various areas of the GreenSock library.

In more detail:

  • By the end of this first part, you’ll have learned about GreenSock’s capabilities and features, licensing model, core components, and basic syntax to tween and stagger DOM elements
  • In part 2, I’ll introduce GreenSock’s native timeline functionality
  • Finally, part 3 will focus on some powerful bonus plugins GreenSock makes available to accomplish complex animation tasks easily with a few lines of code.

If you’re already a GSAP Ninja, check out Animating Bootstrap Carousels with the GSAP Animation Library, where George Martsoukos illustrates an effective use of GreenSock for UI animation.

Without further ado, brace yourself, the journey is about to begin!


What is GreenSock and What Is It Good For?

GreenSock is the de facto industry-standard JavaScript animation platform available today.

It’s a mature JavaScript library that has its roots in Flash-based animation. This means the guys behind GreenSock know web animation inside-out, the library has been around for a long time and is not going anywhere any time soon.

GSAP includes a comprehensive suite of tools, utilities, and plugins you can leverage to handle any web animation challenge you happen to face, from animating SVGs consistently across multiple browsers to coding complex animation sequences, dragging elements across the screen, splitting and scrambling text, and so much more.

To mention just three things I particularly love about GreenSock:

  • Although the library is mega rich in terms of features, the learning curve is relatively shallow because it uses an intuitive and consistent syntax across all its various implementations and plugins. In addition, it offers awesome documentation, tutorials, and support via the GSAP Forums. Also, the library itself is continually updated and maintained. These are all crucial factors when building a project which relies on an external library for any of its key features and user experience
  • It’s modular and light-weight, which means it won’t add bloat to your web projects
  • Thanks to its powerful timeline functionality, GSAP affords precise control over the timings not only of single tweens, but also of multiple tweens as part of a whole animation flow.

Core GreenSock Tools

These are GreenSock’s core modules:

  • TweenLite — the foundation of GSAP, a lightweight and fast HTML5 animation library
  • TweenMax — TweenLite’s extension, which besides comprising TweenLite itself, includes:
    • TimelineLite
    • TimelineMax
    • CSSPlugin
    • AttrPlugin
    • RoundPropsPlugin
    • DirectionalRotationPlugin
    • BezierPlugin
    • EasePack
  • TimelineLite — a lightweight timeline to take control of multiple tweens and/or other timelines
  • TimelineMax — an enhanced version of TimelineLite, which offers additional, non essential capabilities like repeat, repeatDelay, yoyo, and more.

You can choose to include TweenLite in your project and then add other modules separately as you need them. Alternatively, you can choose to include TweenMax (the approach I’m going to take in this multi-part series), which packages all the core modules in one optimized file.

It’s also worth noting that GSAP offers some paid extras like the DrawSVGPlugin to create animated line drawing effects with SVGs, the powerful MorphSVGPlugin to morph one SVG shape into another (even without requiring that the two shapes have the same number of points), and others. Although you need to be a paying member of the Club GreenSock to use these plugins, GSAP makes available to you for free a special CodePen-based version so that you can try them out. This is a cool offer I’m going to take full advantage of later on in part 3 (and you with me).


GSAP hasn’t adopted a free open-source license like MIT largely for reasons that concern keeping the product’s quality high and its maintenance financially sustainable over the long term.

GreenSock makes available two licenses:

  • Standard License — use of the library is totally free in digital products that are free to use (even if developers get paid to build them)
  • Business Green — this license includes three tiers with the middle tier, Shockingly Green, being the most popular. As a Shockingly Green member you’ll gain access to all the bonus plugins and extras, but without the commercial license.

Despite the non-adherence to MIT and similar free use licenses, by letting you peek into its raw code both on the project’s GitHub repo and in your downloads, GreenSock encourages you to learn from its developers’ code and their mastery of JavaScript animation, which is one of the best features of the open source philosophy.

Tweening with GreenSock

A simple animation consists of some kind of change that takes place over time from point A to point B. Animators have a special name for the states in between A and B, i.e., tween.

TweenLite and TweenMax are the two powerful tweening tools GreenSock puts at your disposal. As I said above, I’m going to focus on TweenMax here, but remember that the basic syntax is the same in both libraries.

To load GSAP in your project, add this <script> tag before the closing </body> tag of your HTML document:

<script src=""></script>

You can find the latest version available on the CDN here:

If you use npm, type this in your terminal:

npm install gsap

On CodePen, you’ll find the link to GSAP TweenMax in the Quick add box inside the JavaScript Settings:

CodePen JavaScript Settings box to upload GreenSock TweenMax

A Basic Tween with GreenSock: the Syntax

A simple tween with GSAP looks like this:'.my-element', 1, {opacity: 0});

The snippet above animates a DOM element with the class of my-element from the current default opacity value to the opacity value of 0 over the course of 1 second. In other words, at the end of a 1-second long tween, the element will no longer be visible.

Let’s go into a bit more detail. tells the browser you’re using the to() method of the TweenMax library (the syntax for TweenLite is the same, only replace TweenMax with TweenLite). This method needs a few comma-separated arguments:

  • The element you want to animate (‘.my-element’)
  • The duration of the tween (in this case is 1 second)
  • The vars object {}, that is, the properties you want to tween (in this case the opacity property). This last part goes into curly braces and takes the form of key/value pairs. The value expresses the final state of the tween. There are also other properties you can use inside the vars object {} like callback functions, delays, etc.

As its name suggests, the to() method animates tweenable properties from their default values to what you want those values to be at the end of the animation.

GSAP offers tons of methods, but the core ones besides to() are:

  • from() — lets you decide the starting values in your tween. Therefore the element will animate starting from the values you specify inside from() towards its default values, which are usually those you set in your CSS rules. The syntax looks like this:
    TweenMax.from('.my-element', 1, {opacity: 0});
  • fromTo() — with this method, you specify the values for both the starting point and end point in your tween, which affords closer precision. The syntax is similar to the previous methods, but it includes the vars object{} both for the from (opacity: 1) and to parts (opacity: 0):
    TweenMax.fromTo('.my-element', 1, {
      opacity: 1 // from state
    }, {
      opacity: 0 // to end state

Here are all three methods in action as they are applied on the rotation and translation properties:

See the Pen Basic GreenSock Tweens by SitePoint (@SitePoint) on CodePen.

GSAP breaks away from the CSS syntax by using rotation instead of rotate.

Also, notice that to translate an element along the X or Y axis, GreenSock doesn’t use transform: translateX() or transform: translateY(). Rather, it uses x (as in the live demo), y, xPercent, and yPercent.

While the x and y properties are mostly pixel-based, xPercent and yPercent use percentage values to translate elements along the X and Y axis respectively (CSSPlugin docs).

Finally, keep in mind that to translate the element on the X or Y coordinates, you need to set the element’s CSS position property either to relative or absolute.

Which CSS Properties Does GSAP Animate?

With GreenSock all CSS animatable properties are at your fingertips. You can animate CSS transforms, as discussed above, but also other complex properties such as box-shadow: 1px 1px 1px rgba(0,0,0,0.5) and border: 1px solid red. Just remember to use camelCase wherever the standard CSS property name uses a dash (-), e.g., backgroundColor instead of background-color.

Using GreenSock’s set() Method

If you need to set some properties with specific values before animating them, you can do so either in your CSS or using GreenSock’s set() method. This last option offers the advantage of keeping all your animation-related code in one place, i.e., the JavaScript document.

For instance, the first example in the live demo above starts with the image set in a slightly slanted position. This initial choice is not specified in the CSS document but in the JavaScript document using GSAP’s set() method, like this:

TweenMax.set(toElement, {rotation: -45});

The syntax is the same as a regular tween, but without the duration parameter. This ensures that the change takes place immediately.

Creating Sequences of Tweens with GreenSock

You can create sequences of tweens with GreenSock and coordinate their interaction by adjusting each tween’s duration and delay properties.

For instance, in the code sample below, clicking the Notify Me button triggers the following animation sequence:

  • An input box appears
  • As the input box gets longer, the Notify Me button disappears
  • Finally, a smaller Send button pops into view inside the input box.

Here’s the GSAP code for the sequence (the code goes inside a click handler for the button):

// input box appears and gets bigger, 0.5, {
  autoAlpha: 1,
  scale: 1

// the button being clicked disappears, 1, {
  autoAlpha: 0

// the send button appears and gets bigger, 0.5, {
  autoAlpha: 1,
  scale: 1,
  delay: 0.5,
  ease: Back.easeOut.config(3)

In the snippet you can see two new properties — autoAlpha and ease.

You can use autoAlpha instead of opacity when you need to make sure the element not only disappears from view, but users can’t interact with it. In fact, autoAlpha adds visibility: hidden to opacity: 0.

The ease property lets you choose easings for your animations, which control the rate of change throughout the duration of a tween. This is a crucial ingredient for natural, realistic and smooth animations, and GreenSock offers the Ease Visualizer to give you huge control on the kind of ease that best fits your animation.

GreenSock's Ease Visualizer Tool.

After a few tries, I chose the Back.easeOut ease for this particular tween, but you can have a play and come up with something different.

Here’s the full demo on CodePen:

Watch CSS Animation Tips

Here are some short pointers for you fellow CSS Animators

Staggering Animations with GreenSock

The staggering effect consists in applying the same animation to a group of elements. However, the animation affects each element in succession, that is, one element at a time rather than all elements at once.

GSAP TweenMax offers the staggerTo(), staggerFrom(), and staggerFromTo() methods, which work similarly to the methods discussed above. Only the staggering effect is different, and it requires an extra argument just after the vars object {} to indicate the amount of time you want to elapse between each stagger.

Here’s an example:

TweenMax.staggerFrom(alice, 0.5 {
  rotation: 0,
  delay: 1.5,
  ease: Power4.easeIn
}, 0.5);

In the snippet above, each instance of Alice will rotate from 0 degrees to the values I have set in my CSS with half a second between each rotation:

And here’s the demo using the full code:

See the Pen Simple GSAP stagger method by SitePoint (@SitePoint) on CodePen.

Taking Control of Your GSAP Tweens

GreenSock has a few methods up its sleeve to let you take full control of your tweens.

The ones I’m going to consider here are:

  • play() — plays the animation from wherever the playhead is or from a specific time:
    // plays from the playhead's current location;
    // starts playing from 2 seconds into myAnimation 
    // (all events and callbacks before then don't get fired);
    // starts playing from 2 seconds into myAnimation but
    // doesn't suppress events or callbacks in the initial 
    // part of myAnimation (earlier than 2 seconds), false);
  • pause() — pauses your tween, either completely or starting from a specific point:
    // pauses myAnimation in all its entirety
    // jumps 2 seconds into myAnimation and then pauses
    // jumps 2 seconds into myAnimation then pauses but 
    // doesn't suppress events/callbacks during the 
    // initial phase of the tween (earlier than 2 seconds)
    myAnimation.pause(2, false);
  • reverse() — moves your tween backwards to the initial frame, but you can choose to set a specific time to start from before reversing
    // moves backwards from wherever the playhead currently is
    // moves backwards from exactly 2 seconds into myAnimation 
    // moves backwards from exactly 2 seconds into myAnimation
    // but doesn't suppress events/callbacks before then
    myAnimation.reverse(2, false);
  • restart() — restarts your tween and plays it from the beginning:
    // restarts myAnimation, bypassing any predefined delay
    // restarts myAnimation, including any predefined delay,
    // and doesn't suppress events/callbacks during
    // the initial move back to time:0
    myAnimation.restart(true, false);
  • resume() — resumes playing, either forwards or backwards depending on the current direction of the animation. You can also set the animation to jump to a specific time before resuming it:
    // resumes myAnimation from the playhead's current position
    // jumps to exactly 2 seconds into myAnimation 
    // and then resumes playback:
    // jumps to exactly 2 seconds into myAnimation 
    // and resumes playback but doesn't suppress 
    // events/callbacks during the initial move:
    myAnimation.resume(2, false);

See the Pen Controlling GSAP Tweens by SitePoint (@SitePoint) on CodePen.

It’s impossible to list all methods GSAP’s TweenLite and TweenMax make available to you. Therefore, I encourage you to check out the docs — they’re super friendly.

TweenMax yoyo, repeat, and repeatDelay

I’d like to close this first article dedicated to GreenSock with three useful features you can use in your TweenMax-powered animations:

  • repeat — use this if you want your tween to play a set number of times or indefinitely. In this last case, set repeat to the value of -1:
    // the tween repeats 3 times on top of the default 
    // time (4 times overall):, 1, { 
      opacity: 0,
      repeat: 3 
  • repeatDelay — you can use this property to set a specific delay between each of your animation’s repetitions:
    // the tween repeats 3 times on top of the default 
    // time (4 times overall) with one a second delay 
    // between each repetition:, 1, { 
      opacity: 0,
      repeat: 3,
      repeatDelay: 1 
  • yoyo — is very handy when you want your animation to go back and forth a set number of times, or indefinitely. Use it in conjunction with repeat to create movements that alternate between two states:
    // the tween repeats indefinitely with one second's delay 
    // between each repetition. The element alternates 
    // between being fully opaque and fully transparent:, 1, { 
      opacity: 0,
      repeat: -1,
      repeatDelay: 1 


In this first part dedicated to the GreenSock library, I’ve discussed what GreenSock excels at, its capabilities, core components, and licensing model.

I’ve also introduced you to GSAP’s basic syntax for tweening DOM elements with TweenMax using a number of live demos.

However, although you can create some cool animations just sequencing GSAP tweens, there are a couple of shortcomings to this approach:

  • If you change a tween’s duration or delay in a sequence of tweens, it’s likely most of the overall animation will be messed up and in need of further adjustments
  • A sequence of tweens is made up of independent tweens, therefore you can’t pause, resume, reverse, etc. the entire sequence as a whole.

To give you extra control, GSAP offers robust and flexible timeline functionality, which I’ll be discussing in the second instalment dedicated to this awesome library.

Have you used GreenSock in your web animation work? I’d love to see what you’ve created with it.

If you’re curious about JavaScript-based animation and performance, the JS with Performance: requestAnimationFrame screencast is available to all SitePoint Premium members.

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