Thursday, 12 April, 2018 UTC
Summary
React Motion is a popular library for animations in React. It makes use of physics to create animations that feel natural. All we have to do to create realistic animations is provide values for stiffness and damping and React Motion takes care of the rest.
In this post we’ll go over the basics of using the library to animate the scaling of a simple Card component. We’ll make use of styled-components for our Card’s styling. We’ll then go over a simple example of animating components as a function of state.
Installation Just add the react-motion package to your project using npm or Yarn. Here we’ll also make use of styled-component, so we’ll add that too:
$ yarn add react-motion styled-components # or $ npm install react-motion styled-components To create a simple demo, our App component will just render two Card components:
App.js
import React, { Component } from 'react'; import { injectGlobal } from 'styled-components'; import Card from './Card'; injectGlobal` body { margin: 0; background: #fbfbfb; } `; class App extends Component { render() { return ( <React.Fragment> <Card /> <Card title="😎 Fancy!" content="Nothing to say" /> </React.Fragment> ); } } export default App; Notice how we can use style-component's injectGlobal to inject some global styles.
And here’s all the components that make up our Card component:
Card.js
import React from 'react'; import styled from 'styled-components'; const CardWrapper = styled.div` background: #fff; max-width: 500px; margin: 2rem auto; box-shadow: 0 0 10px rgba(0, 0, 0, 0.1); border-radius: 5px; `; const FooterWrapper = styled.div` border-top: 2px solid #f7f7f7; padding: 1rem 0; text-align: center; `; const HeaderWrapper = styled.div` background-image: url('/palm-trees.jpg'); min-height: 150px; color: white; text-shadow: 0 2px 5px rgba(0, 0, 0, 0.3); background-size: 100%; background-position: 50%; display: flex; justify-content: flex-end; align-items: flex-end; padding: 1rem; `; const MainWrapper = styled.div` padding: 1rem; `; const Button = styled.button` background-image: linear-gradient(to bottom, #fff, #f3f3f3); border-radius: 8px; letter-spacing: 1px; padding: 10px 20px; margin: 0 0.45rem; border: 1px solid #ddd; box-shadow: 0 0 10px rgba(0, 0, 0, 0.1); &:active { background: #eee; } `; const Header = ({ title }) => { return ( <HeaderWrapper> <h1>{title}</h1> </HeaderWrapper> ); }; const Main = ({ content }) => { return ( <MainWrapper> <p>{content}</p> </MainWrapper> ); }; const Footer = () => { return ( <FooterWrapper> <Button>View</Button> <Button>Save for later</Button> </FooterWrapper> ); }; class Card extends React.Component { render() { const { title, content } = this.props; return ( <CardWrapper> <Header title={title} /> <Main content={content} /> <Footer /> </CardWrapper> ); } } Card.defaultProps = { title: 'My card title', content: 'Bacon ipsum dolor amet pork chop pork shoulder.' }; export default Card; Our cards look like this:
Now, say we can to animate the cards in when they first mount. Let’s use React Motion’s Motion component to accomplish this:
App.js
// ... import { Motion, spring } from 'react-motion'; import Card from './Card'; // ... const AnimatedCard = props => { return ( <Motion defaultStyle={{ scale: 0.5 }} style={{ scale: spring(1, { stiffness: 60, damping: 10 }) }} > {interpolatedStyle => <Card scale={interpolatedStyle.scale} {...props} />} </Motion> ); }; class App extends Component { render() { return ( <React.Fragment> <AnimatedCard /> <AnimatedCard title="😎 Fancy!" content="Nothing to say" /> </React.Fragment> ); } } export default App; As you can see, the Motion component makes use of the render prop pattern. It expects a function as its children prop and the function receives the
interpolatedStyle that contains the current interpolated values. Here we pass the interpolated scale value to a scale prop.We can make use of this scale prop in our style-component like this:
Card.js
// ... const CardWrapper = styled.div` background: #fff; max-width: 500px; margin: 2rem auto; box-shadow: 0 0 10px rgba(0, 0, 0, 0.1); border-radius: 5px; transform: ${props => `scale(${props.scale})`}; `; // ... class Card extends React.Component { render() { const { title, content, scale } = this.props; return ( <CardWrapper scale={scale}> <Header title={title} /> <Main content={content} /> <Footer /> </CardWrapper> ); } } // ... The Motion component takes an optional defaultStyle prop and a required style prop. The style prop is derived using the spring helper function. Spring takes a value to spring to, and an optional config object with values for stiffness, damping and precision. When no config object is passed to spring, the stiffness defaults to 170 and the damping defaults to 26.
In the previous example we pass a scale prop that then gets used by a styled-component, but we could just as well animate inline styles. Here for example we render a h1 element that springs into view:
const FancyTitle = () => { return ( <Motion defaultStyle={{ left: -100 }} style={{ left: spring(10) }}> {val => <h1 style={{ position: 'absolute', ...val }}>Hello!{' '} <span role="img" aria-label="Hand wave"> 👋 </span> </h1>} </Motion> ); }; Using React Motion makes it just as easy to define animations that are a function of the state.
In the following example, we first animate our h1 element into view when the App component mounts, and then provide buttons that call methods to change the state, which controls the animation on the element:
import React, { Component } from 'react'; import { Motion, spring } from 'react-motion'; class App extends Component { state = { left: 0 }; handleClick = val => { if (val && !isNaN(val)) { this.setState({ left: +val }); } }; reset = () => this.setState({ left: 0 }); render() { return ( <React.Fragment> <Motion defaultStyle={{ left: -100 }} style={{ left: spring(this.state.left) }} > {val => ( <h1 style={{ position: 'absolute', ...val }}> Hello!{' '} <span role="img" aria-label="Hand wave"> 👋 </span> </h1> )} </Motion> <input type="number" placeholder="enter a value" ref={input => (this.input = input)} /> <button onClick={() => this.handleClick(this.input.value)}>Set</button> <button onClick={this.reset}>Reset</button> </React.Fragment> ); } } export default App; 💃 Now go ahead and make things move! In a future post we'll explore the rest of the API made available with React Motion (StaggeredMotion, TransitionMotion and presets).