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You can define a "modifier" function for almost any property; this modifier intercepts the value that GSAP would normally apply on each update ("tick"), feeds it to your function as the first parameter and lets you run custom logic, returning a new value that GSAP should then apply. This is perfect for tasks like snapping, clamping, wrapping, or other dynamic effects. It's completely up to you! Parameters: value, target The modifier functions are passed two parameters: value (number | string) - The about-to-be-applied value from the regular tween. This is often a number, but could be a string based on whatever the property requires. For example if you're animating the x property, it would be a number, but if you're animating the left property it could be something like "212px", or for the boxShadow property it could be "10px 5px 10px rgb(255,0,0)". target (object) - The target itself. For example, change the x of one object based on the y of another object or change rotation based on the direction it is moving. Below are some examples that will help you get familiarized with the syntax. Snap rotation The tween below animates 360 degrees but the modifier function forces the value to jump to the closest 45-degree increment. Take note how the modifier function gets passed the value of the property that is being modified, in this case a rotation number. This is a good example of the ModifiersPlugin, but as of GSAP 3 you should probably be using GSAP's SnapPlugin for this sort of thing: Clamp with Modulus The tween below animates x to 500 but the modifier function forces the value to wrap so that it's always between 0 and 100. This is a good example of the ModifiersPlugin, but as of GSAP 3 you should probably be using GSAP's SnapPlugin for this sort of thing: Carousel Wrap Have you ever built a carousel and wrestled with making it loop seamlessly? Perhaps you duplicated each asset or wrote some code that moved each item back to the beginning when it reached the end. With ModifiersPlugin you can get a seamless repeating carousel with a single tween! The example below tweens each box to a relative x position of "+=500". Click the "show overflow" button to see each box get reset to x:0 when it goes beyond 500... Advanced demos We've only scratched the surface of what ModifiersPlugin can do. Our moderator Blake Bowen has been putting this new plugin to the test and has an impressive collection of demos that will surely inspire you. View the docs for ModifiersPlugin.

Note: This page was created for GSAP version 2. We have since released GSAP 3 with many improvements. While it is backward compatible with most GSAP 2 features, some parts may need to be updated to work properly. Please see the GSAP 3 release notes for details. GSAP version 1.19.0 introduces some exciting new features for advanced users as well as conveniences for everyone (even the "greenest" novices). The most noteworthy improvements are summarized below: Function-based values Instead of a number (x:100) or string (width:"300px") or relative value (y:"+=50"), you can now define most values as a function that'll get called once for each target the first time the tween renders, and whatever is returned by that function will be used as the value. This can be very useful for randomizing things or applying conditional logic. See it in action in the demos below. See the Pen BzmGba by GreenSock (@GreenSock) on CodePen. ...and more GSAP 1.19.0 is more ES6-friendly (for example, you can npm install gsap and then import {TweenLite, Elastic, TimelineMax} from "gsap" in your project). Plenty of bug fixes too. See the whole list in the github changelog. DOWNLOAD GSAP TODAY Happy tweening!