React-Motion
import {Motion, spring} from 'react-motion';
<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
{
"dependencies": {
"react-motion": "https://npmcdn.com/react-motion/bower.zip"
}
}
then include as
<script src="bower_components/react-motion/build/react-motion.js"></script>
<script src="https://npmcdn.com/react-motion/build/react-motion.js"></script>
(Module exposed as `ReactMotion`)
- Build it yourself from the repo:
git clone https://github.com/chenglou/react-motion.git
cd react-motion
npm install
npm run prerelease
To try the demos locally with hot reloading, run npm start
. Don't forget to compile for production when you test your animation's performance!
For React-native: previous react-motion v0.3.* supported a dedicated build for RN, which has now been made obsolete since RN v0.18. This library should Just Work under the new React-Native 0.18+.
Demos
Check the wiki for more!
What does this library try to solve?
My React-Europe talk
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
Coming from 0.3. to 0.4.0? Here's the upgrade guide.*
Exports:
spring
.Motion
StaggeredMotion
TransitionMotion
presets
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).
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 to 170
.damping
: optional, defaults to 26
.precision
: optional, defaults to 0.01
. 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
OpaqueConfig
returned from spring(x)
: interpolate to x
. - a
number
x
: jump to x
, do not interpolate.
- defaultStyle?: PlainStyle
Optional. The PlainStyle
type maps to number
s. 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 gave style={{x: spring(10), y: spring(20)}}
, you'll receive as interpolatedStyle
, at a certain time, {x: 5.2, y: 12.1}
, which you can then apply on your div
or something else.
-
Return: must return one React element to render.
<StaggeredMotion />
Animates a collection of 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 (undefined
at first render, unless defaultStyles
is provided).
-
Return: must return an array of Style
s 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}]
<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.
const Demo = React.createClass({
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}],
});
},
willLeave() {
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: any, data?: any, style: Style}
.
-
key
: required. The ID that TransitionMotion
uses to track which configuration is which across renders, even when things are reordered. Typically reused as the component key
when you map over the interpolated styles.
-
data
: optional. Anything you'd like to carry along. This is so that when the previous section example's c
disappears, you still get to access c
's related data, such as the text to display along with it.
-
style
: required. The actual starting style configuration, similar to what you provide for Motion
's style
. Maps keys to either a number or an OpaqueConfig
returned by spring()
.
-
TransitionPlainStyle
: similar to above, except the style
field's value is of type PlainStyle
, aka an object that maps to numbers.
- styles: Array<TransitionStyle> | (previousInterpolatedStyles: ?Array<TransitionPlainStyle>) => Array<TransitionStyle>
Required. Accepts either:
-
an array of TransitionStyle
configs, e.g. [{key: 1, style: {x: spring(0)}}, {key: 2, style: {x: spring(10)}}]
.
-
a function similar to StaggeredMotion
, taking the previously interpolating styles (undefined
at first call, unless defaultStyles
is 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: ..., value: ...}
object from the styles
array, identified by key
, that was present during a previous render, and that is now absent, thus triggering the call to willLeave
.
-
Return: null
to indicate you want the TransitionStyle
gone immediately. A Style
object to indicate you want to reach transition to the specified value(s) before killing the TransitionStyle
.
- willEnter?: (styleThatEntered: TransitionStyle) => PlainStyle
Optional. Defaults to styleThatEntered => stripStyle(styleThatEntered.style)
. Where stripStyle
turns {a: spring(10), b: spring(20)}
into {a: 10, b: 20}
.
-
styleThatEntered
: similar to willLeave
's, except the TransitionStyle
represents the object whose key
value was absent during the last render
, and that is now present.
-
Return: a defaultStyle
-like PlainStyle
configuration, e.g. {a: 0, b: 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.
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
TransitionMotion
container 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
ref
doesn'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.