React-Motion

import {Motion, spring} from 'react-motion'; // In your render...<motion defaultstyle="{{x:" style="{{x:" spring>
  {value =&gt; <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**. Use

bower install --save https://unpkg.com/react-motion/bower.zip

. Or in

bower.json

:

json { "dependencies": { "react-motion": "https://unpkg.com/react-motion/bower.zip" } }

then include as

html<script src="bower_components/react-motion/build/react-motion.js"></script>

• 1998 Script Tag:

html<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

Check the wiki for more!

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-demos

  and open the static

  demos/demo\_name/index.html

  file 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?

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

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).

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 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:" style="{{x:" spring>
  {interpolatingStyle =&gt; <div style="{interpolatingStyle}"></div>}
</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.

- 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:" styles="{prevInterpolatedStyles"> prevInterpolatedStyles.map((_, i) =&gt; {
    return i === 0
      ? {h: spring(100)}
      : {h: spring(prevInterpolatedStyles[i - 1].h)}
  })}&gt;
  {interpolatingStyles =&gt;
    <div>
      {interpolatingStyles.map((style, i) =&gt;
        <div key="{i}" style="{{border:" solid height: style.h></div>)
      }
    </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}]

(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},
        }))}&gt;
        {interpolatedStyles =&gt;
          // first render: a, b, c. Second: still a, b, c! Only last one's a, b.
          <div>
            {interpolatedStyles.map(config =&gt; {
              return <div key="{config.key}" style="{{...config.style," border: solid></div>
            })}
          </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 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: 'a', style: {x: spring(0)}}, {key: 'b', 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: ..., style: ...}

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

. Note that the style property is exactly what you passed in

styles

, and is not interpolated. For example, if you passed a spring for

x

you will receive an object like

{x: {stiffness, damping, val, precision}}

.

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

.

- 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 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.

{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

  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

](https://github.com/chenglou/react-motion/blob/master/#staggeredmotion-)

• My

  ref

  doesn't work in the children function.

React string refs won't work:

<motion style="{...}">{currentValue =&gt; <div ref="stuff"></div>}</motion>

This is how React works. Here's the callback ref solution.