GreenSock (GSAP) basics - Web Animation in your browser

What exactly is a tween?

The first time I heard the word "tween", I wasn't totally sure what it meant. Simply put, a tween is a sequence of frames. In a digital context, basically a tween is an animation.

So how do we make them?

Luckily for us, lots of libraries exist to help us utilize tweens in the browser. One such library is GreenSock. Today, we will learn about .to() and .from(), and get you tweening in no time.

Firstly, grab GreenSock from a CDN, and place it in a <script> tag in your HTML. Remember to place it before your normal javascript file.

<script src=""></script>

Check the latest version on their homepage

The CDN will provide you with a gsap object which you can console.log(gsap), and take a look at the various methods it provides. Today, we will be looking at tweens from the "core" property.

Dev tools view of GreenSock object


Our first tween is It takes two parameters.

  1. The target - It can be a normal CSS selector.
  2. An object containing properties and values to animate."svg:last-child", {
  duration: 1,
  x: 100,

If you don't specify a unit value, gsap will animate pixels. The default duration time is 0.5 seconds.

One important note is that values on .to() will be the final position of the tween, while CSS values will be starting position.

Take a look at it in action on codepen.


Being the opposite of .to(), our gsap values will be the starting point, and our CSS positions will be the destination. Let's animate background colour. When using double-barreled property words, we use the camelCasing naming convention to declare them in gsap.

gsap.from(".square", {
  backgroundColor: "green",
  delay: 2,

Using a delay of 2 means the animation will begin 2 seconds after the page loads.


I thought we were only going to look at two tweens? Well, technically yes. .fromTo() as you can imagine is a combination of both. Remember how our CSS defined our start or end position before? This tween allows us to define both in gsap. Here, we pass an object for both our from and to values.

With .fromTo(), we add our special properties like duration to the 2nd object, which is our to properties/vars.

gsap.fromTo(".square", { x: 50 }, { x: 0, duration: 1 });

GreenSock is a really powerful animation library. While there is a paid tier, lots of functionality is available for free to use in your projects. It is also possible to use the paid tier functionality on for free. I hope this post helped you get started with tweens.