JarCastingReact-Motion
import {Motion, spring} from 'react-motion';
// In your render...
<Motion defaultStyle={{x: 0}} style={{x: spring(10)}}>
{value => <div>{value.x}</div>}
</Motion>
Animate a counter from 0 to 10. For more advanced usage, see below.
Install
-
Npm:
npm install --save react-motion -
Bower: do not install with
bower install react-motion, it won't work. Usebower install --save https://unpkg.com/react-motion/bower.zip. Or inbower.json:
{
"dependencies": {
"react-motion": "https://unpkg.com/react-motion/bower.zip"
}
}
then include as
<script src="bower_components/react-motion/build/react-motion.js"></script>
- 1998 Script Tag:
<script src="https://unpkg.com/react-motion/build/react-motion.js"></script>
(Module exposed as `ReactMotion`)
Works with React-Native v0.18+.
Demos
- Simple Transition
- Chat Heads
- Draggable Balls
- TodoMVC List Transition
- Photo Gallery
- Spring Parameters Chooser
- Water Ripples
- Draggable List
Try the Demos Locally
git clone https://github.com/chenglou/react-motion.git
cd react-motion
npm install
- With hot reloading (slow, development version): run
npm start. - Without hot reloading (faster, production version): run
npm run build-demosand open the staticdemos/demo_name/index.htmlfile directly. Don't forget to use production mode when testing your animation's performance!
To build the repo yourself: npm run prepublish.
What does this library try to solve?
For 95% of use-cases of animating components, we don't have to resort to using hard-coded easing curves and duration. Set up a stiffness and damping for your UI element, and let the magic of physics take care of the rest. This way, you don't have to worry about petty situations such as interrupted animation behavior. It also greatly simplifies the API.
This library also provides an alternative, more powerful API for React's TransitionGroup.
API
Exports:
springMotionStaggeredMotionTransitionMotionpresets
Here's the well-annotated public Flow type definition file (you don't have to use Flow with React-motion, but the types help document the API below).
P.S. using TypeScript? Here are the React-motion TypeScript definitions!
Helpers
- spring: (val: number, config?: SpringHelperConfig) => OpaqueConfig
Used in conjunction with the components below. Specifies the how to animate to the destination value, e.g. spring(10, {stiffness: 120, damping: 17}) means "animate to value 10, with a spring of stiffness 120 and damping 17".
-
val: the value. -
config: optional, for further adjustments. Possible fields:stiffness: optional, defaults to170.damping: optional, defaults to26.precision: optional, defaults to0.01. Specifies both the rounding of the interpolated value and the speed (internal).
It's normal not to feel how stiffness and damping affect your spring; use Spring Parameters Chooser to get a feeling. Usually, you'd just use the list of tasteful stiffness/damping presets below.
- Presets for {stiffness, damping}
Commonly used spring configurations used like so: spring(10, presets.wobbly) or spring(20, {...presets.gentle, precision: 0.1}). See here.
<Motion />
Usage
<Motion defaultStyle={{x: 0}} style={{x: spring(10)}}>
{interpolatingStyle => <div style={interpolatingStyle} />}
</Motion>
Props
- style: Style
Required. The Style type is an object that maps to either a number or an OpaqueConfig returned by spring() above. Must keep the same keys throughout component's existence. The meaning of the values:
- an
OpaqueConfigreturned fromspring(x): interpolate tox. - a
numberx: jump tox, do not interpolate.
- defaultStyle?: PlainStyle
Optional. The PlainStyle type maps to numbers. Defaults to an object with the same keys as style above, whose values are the initial numbers you're interpolating on. Note that during subsequent renders, this prop is ignored. The values will interpolate from the current ones to the destination ones (specified by style).
- children: (interpolatedStyle: PlainStyle) => ReactElement
Required function.
-
interpolatedStyle: the interpolated style object passed back to you. E.g. if you gavestyle={{x: spring(10), y: spring(20)}}, you'll receive asinterpolatedStyle, at a certain time,{x: 5.2, y: 12.1}, which you can then apply on yourdivor something else. -
Return: must return one React element to render.
- onRest?: () => void
Optional. The callback that fires when the animation comes to a rest.
<StaggeredMotion />
Animates a collection of (fixed length) items whose values depend on each other, creating a natural, springy, "staggering" effect like so. This is preferred over hard-coding a delay for an array of Motions to achieve a similar (but less natural-looking) effect.
Usage
<StaggeredMotion
defaultStyles={[{h: 0}, {h: 0}, {h: 0}]}
styles={prevInterpolatedStyles => prevInterpolatedStyles.map((_, i) => {
return i === 0
? {h: spring(100)}
: {h: spring(prevInterpolatedStyles[i - 1].h)}
})}>
{interpolatingStyles =>
<div>
{interpolatingStyles.map((style, i) =>
<div key={i} style={{border: '1px solid', height: style.h}} />)
}
</div>
}
</StaggeredMotion>
Aka "the current spring's destination value is the interpolating value of the previous spring". Imagine a spring dragging another. Physics, it works!
Props
- styles: (previousInterpolatedStyles: ?Array<PlainStyle>) => Array<Style>
Required function. Don't forget the "s"!
-
previousInterpolatedStyles: the previously interpolating (array of) styles (undefinedat first render, unlessdefaultStylesis provided). -
Return: must return an array of
Styles containing the destination values, e.g.[{x: spring(10)}, {x: spring(20)}].
- defaultStyles?: Array<PlainStyle>
Optional. Similar to Motion's defaultStyle, but an array of them.
- children: (interpolatedStyles: Array<PlainStyle>) => ReactElement
Required function. Similar to Motion's children, but accepts the array of interpolated styles instead, e.g. [{x: 5}, {x: 6.4}, {x: 8.1}]
(No onRest for StaggeredMotion because we haven't found a good semantics for it yet. Voice your support in the issues section.)
<TransitionMotion />
Helps you to do mounting and unmounting animation.
Usage
You have items a, b, c, with their respective style configuration, given to TransitionMotion's styles. In its children function, you're passed the three interpolated styles as params; you map over them and produce three components. All is good.
During next render, you give only a and b, indicating that you want c gone, but that you'd like to animate it reaching value 0, before killing it for good.
Fortunately, TransitionMotion has kept c around and still passes it into the children function param. So when you're mapping over these three interpolated styles, you're still producing three components. It'll keep interpolating, while checking c's current value at every frame. Once c reaches the specified 0, TransitionMotion will remove it for good (from the interpolated styles passed to your children function).
This time, when mapping through the two remaining interpolated styles, you'll produce only two components. c is gone for real.
import createReactClass from 'create-react-class';
const Demo = createReactClass({
getInitialState() {
return {
items: [{key: 'a', size: 10}, {key: 'b', size: 20}, {key: 'c', size: 30}],
};
},
componentDidMount() {
this.setState({
items: [{key: 'a', size: 10}, {key: 'b', size: 20}], // remove c.
});
},
willLeave() {
// triggered when c's gone. Keeping c until its width/height reach 0.
return {width: spring(0), height: spring(0)};
},
render() {
return (
<TransitionMotion
willLeave={this.willLeave}
styles={this.state.items.map(item => ({
key: item.key,
style: {width: item.size, height: item.size},
}))}>
{interpolatedStyles =>
// first render: a, b, c. Second: still a, b, c! Only last one's a, b.
<div>
{interpolatedStyles.map(config => {
return <div key={config.key} style={{...config.style, border: '1px solid'}} />
})}
</div>
}
</TransitionMotion>
);
},
});
Props
First, two type definitions to ease the comprehension.
-
TransitionStyle: an object of the format{key: string, data?: any, style: Style}.-
key: required. The ID thatTransitionMotionuses to track which configuration is which across renders, even when things are reordered. Typically reused as the componentkeywhen you map over the interpolated styles. -
data: optional. Anything you'd like to carry along. This is so that when the previous section example'scdisappears, you still get to accessc's related data, such as the text to display along with it. -
style: required. The actual starting style configuration, similar to what you provide forMotion'sstyle. Maps keys to either a number or anOpaqueConfigreturned byspring().
-
-
TransitionPlainStyle: similar to above, except thestylefield's value is of typePlainStyle, aka an object that maps to numbers.
- styles: Array<TransitionStyle> | (previousInterpolatedStyles: ?Array<TransitionPlainStyle>) => Array<TransitionStyle>
Required. Accepts either:
-
an array of
TransitionStyleconfigs, e.g.[{key: 'a', style: {x: spring(0)}}, {key: 'b', style: {x: spring(10)}}]. -
a function similar to
StaggeredMotion, taking the previously interpolating styles (undefinedat first call, unlessdefaultStylesis provided), and returning the previously mentioned array of configs. You can do staggered mounting animation with this.
- defaultStyles?: Array<TransitionPlainStyle>
Optional. Similar to the other components' defaultStyle/defaultStyles.
- children: (interpolatedStyles: Array<TransitionPlainStyle>) => ReactElement
Required function. Similar to other two components' children. Receive back an array similar to what you provided for defaultStyles, only that each style object's number value represent the currently interpolating value.
- willLeave?: (styleThatLeft: TransitionStyle) => ?Style
Optional. Defaults to () => null. The magic sauce property.
-
styleThatLeft: the e.g.{key: ..., data: ..., style: ...}object from thestylesarray, identified bykey, that was present during a previous render, and that is now absent, thus triggering the call towillLeave. Note that the style property is exactly what you passed instyles, and is not interpolated. For example, if you passed a spring forxyou will receive an object like{x: {stiffness, damping, val, precision}}. -
Return:
nullto indicate you want theTransitionStylegone immediately. AStyleobject to indicate you want to reach transition to the specified value(s) before killing theTransitionStyle.
- didLeave?: (styleThatLeft: {key: string, data?: any}) => void
Optional. Defaults to () => {}.
styleThatLeft: the{key:..., data:...}that was removed after the finished transition.
- willEnter?: (styleThatEntered: TransitionStyle) => PlainStyle
Optional. Defaults to styleThatEntered => stripStyle(styleThatEntered.style). Where stripStyle turns {x: spring(10), y: spring(20)} into {x: 10, y: 20}.
-
styleThatEntered: similar towillLeave's, except theTransitionStylerepresents the object whosekeyvalue was absent during the lastrender, and that is now present. -
Return: a
defaultStyle-likePlainStyleconfiguration, e.g.{x: 0, y: 0}, that serves as the starting values of the animation. Under this light, the default provided means "a style config that has the same starting values as the destination values".
Note that willEnter and defaultStyles serve different purposes. willEnter only triggers when a previously inexistent TransitionStyle inside styles comes into the new render.
(No onRest for TransitionMotion because we haven't found a good semantics for it yet. Voice your support in the issues section.)
FAQ
- How do I set the duration of my animation?
Hard-coded duration goes against fluid interfaces. If your animation is interrupted mid-way, you'd get a weird completion animation if you hard-coded the time. That being said, in the demo section there's a great Spring Parameters Chooser for you to have a feel of what spring is appropriate, rather than guessing a duration in the dark.
- How do I unmount the
TransitionMotioncontainer itself?
You don't. Unless you put it in another TransitionMotion...
- How do I do staggering/chained animation where items animate in one after another?
See StaggeredMotion
- My
refdoesn't work in the children function.
React string refs won't work:
<Motion style={...}>{currentValue => <div ref="stuff" />}</Motion>
This is how React works. Here's the callback ref solution.