Micro Animation Helper

A framework agnostic light shim over the Web Animation API to swiftly create awaitable micro animations from JS.

Why

Javascript is an event driven language and UI is state driven. Transitions between different states in the UI are driven by events. So should the transition be defined by CSS and the UI as it is most commonly done today, or should it be done by Javascript? One way of looking at it is: what solution generates less lines of code. And if that is the case I'd say Javascript mostley wins.

Often times using transitions in the CSS creates constant custom CSS code for every animation, hard to parse and prone to timing problem between CSS timing and JS. By moving the transitions from CSS to JS the result is both cleaner and less code and in perfect sync with other JS events as a result. It is obvious that micro animation belongs in JavaScript and not in CSS. Specially when there is a need to chain events.

The Web Animation API is powerfull but clunky. The microAnimation helper is all you need for your micro animation one liners.

Install

npm install @foundit/micro-animation

Usage

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import { microAnimation } from '@foundit/micro-animation'

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Minimum is to pass an element and a transformEnd object containing the properties you want to animate to. Animation start state is then picked up from the element's computed style. There is a possibility to set an initial state by transitionInit argument but unless there is a special reason avoid it to avoid jankiness when the animation is canceled and restarted in quick succession.

``js
async function closeModal() {
await microAnimation({
element: myModalElement,
duration: 300,
transformEnd: { opacity: 0 },
})
removeElement()
}
`

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The underlying Web Animation API blurs the differences between CSS transitions and keyframe animation. So we do too 🙂 For a keyframe animation, pass an array of keyframe objects. The offset property is optional, defaults to splitting equally between frames. In the example below, the background color will change to orangered at 70% of the animation. The keyframes will equally share the duration if the middle keyframe(s) offset key is omitted.

`js
...
await microAnimation({
element: myAnimatedElement,
duration: 1000,
easing: 'ease-out',
transformEnd: [{
backgroundColor: 'orangered',
opacity: 1, offset: 0.7
}, {
transform: "translateX(0)",
backgroundColor: 'blue'
}]
})
...
`

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In general you should not use a initial state. Having a start state might cause jankiness when the animation is interupted/restarted in quick succession. Which normally is not a problem since the start state is created dynamically from the computed style. But if you would really need a set start state you can use the transitionInit property.

`js
async function openModal() {
// create and execute a micro animation with a set start state style
// the myModal element fades in and slides upp 10px
// run you micro animation
void microAnimation({
element: myModal,
duration: 300,
easing: 'ease-in',
transitionInit: {
translate: '0 10px',
opacity: 0,
},
transformEnd: { translate: '0 0'; opacity: 0 },
})
}
`

Use void instead of await if you don't need to wait for the promise to resolve. Handy if you need to execute it directly inside a useEffect in React where you can't have await. It is also _thenable_ should you prefer that to await.

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- duration - duration of the total nimation in ms
- easing - any of the easings available in CSS, i.e 'ease-in', 'linear', etc
- element\* - a DOM element or ref element if your using React. Can also be more than one, then passed in a array.
- fill - same function as fillMode in CSS, defaults to 'forward'
- pseudoElement - Accepts a string with your pseudo element. E.g '::after'
- composite - takes 'replace', 'add' or 'accumulate'. See mdncomposite for explanation.
- transformEnd\* - a keyframe object or array of keyframe objects containg animatable CSS properties in camel case with its corresponding values
- transformInit - Keyframe object with CSS properties to start the animation from. Recommended to omit to use computed style as starting point.

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A keframe object is an object with camel cased css properties as keys with values.

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This little helper is built in Typescript. MicroAnimationProps, TargetElement are exported. The keyframe object is a Keyframe` type.

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Links: NPM | Github Issues | Web Animation API MDN | Codepen

Author: nicolas@hervy.se