Popmotion is:

• Powerful: It supports keyframe and spring animations for numbers, colors and complex strings.
• Low level: It's designed to be composable and portable into any JavaScript environment, with an eye on worklets in the future.
• Stable: It's written in TypeScript and enjoys over 95% test coverage.
• Tiny: animate is just ~4.5kb, and every function is individually importable.

npm install popmotion

import { animate } from "popmotion"

animate({
  from: 0,
  to: 100,
  onUpdate: latest => console.log(latest)
})

animate performs a keyframes or spring animation.

import { animate } from "popmotion"

animate({
  from: 0, 
  to: 100,
  onUpdate: latest => console.log(latest)
})

It can animate numbers:

animate({ from: 0, to: 100 })

Or strings of the same type:

animate({ from: "0px", to: "100px" })
animate({ from: "#fff", to: "#000" })

The strings can be pretty complex, for instance box shadows or SVG path definitions. The only limitation is that the numbers and colors contained within must be in the same order:

animate({
  from: "0px 0px 0px rgba(0, 0, 0, 0)",
  to: "10px 10px 0px rgba(0, 0, 0, 0.2)"
})

The type of animation performed will be automatically detected from the provided options, or can be chosen manually by defining type as "keyframes", "spring" or "decay".

These options can be set for all animations:

An initial value to start the animation from.

Defaults to 0

animate({
  from: "linear-gradient(#e66465, #9198e5)",
  to: "linear-gradient(#9198e5, #e66465)"
})

Sets an initial elapsed time, in milliseconds. Set to a negative value for a delay.

animate({
  to: 100,
  elapsed: -300
})

The number of times to repeat the animation. Set to Infinity to repeat forever.

animate({
  to: 100,
  repeat: 2
})

The duration, in milliseconds, to wait before repeating the animation.

animate({
  to: 100,
  repeat: 2,
  repeatDelay: 200
})

Either "loop", "mirror" or "reverse". Defaults to "loop".

• "loop": Repeats the animation from 0.
• "mirror": Swaps the from/to values alternately.
• "reverse": Reverses the animation alternately.

animate({
  to: 100,
  repeat: 2,
  repeatType: "reverse"
})

By default, the animation will be driven by a requestAnimationFrame loop. driver can specify a different source.

A Driver is a function that accepts the animations update function. This is a function that can be called with a time delta from the previous frame. The Driver must return a function that will be called when the animation is stopped.

const xrDriver = session => update => {
  let latestRequestId = 0
  let prevTimestamp = performance.now()
  
  const step = timestamp => {
    const delta = timestamp - prevTimestamp
    prevTimestamp = timestamp

    update(delta)

    latestRequestId = session.requestAnimationFrame(step)
  }

  let latestRequestId = session.requestAnimationFrame(step)

  return () => session.cancelRequestAnimationFrame(latestRequestId)
}

animate({
  to: 100,
  driver: xrDriver(xrSession)
})

animate will automatically detect the type of animation to use based on the options provided. But a specific type can be chosen manually by defining type as "keyframes", "spring" or "decay".

animate({
  to: 100,
  type: "spring"
})

The following lifecycle events are available for all animations:

This is called every frame the animation fires with the latest computed value.

animate({
  to: 100,
  onUpdate: latest => console.log(latest)
})

This is called when the animation starts. Currently this automatically when animate is called.

animate({
  to: 100,
  onPlay: () => {}
})

This is called when the animation successfully completes.

animate({
  to: 100,
  onComplete:() => {}
})

This is called when an animation repeats.

animate({
  to: 100,
  repeat: 2,
  onRepeat: () => {}
})

This is called when the animation is stopped by the stop control.

const animation = animate({
  to: 100,
  onStop: () => {}
})

animation.stop()

A keyframes animation is the default animation type and it can be defined either with a from and to option:

animate({ from: 0, to: 100 })

Or as a series of keyframes provided to the to option:

animate({ to: [0, 100, 200] })

A single value to animate to, or an array of values to animate through.

animate({
  to: ["#0ff", "#f00", "#0f0"]
})

If to is an array, any defined from will be ignored.

This defines the duration of the animation, in milliseconds.

animate({
  to: 100,
  duration: 300
})

This is an easing function, or array of functions, to use when easing between each keyframe.

import { animate, linear, easeInOut } from "popmotion"

animate({
  to: 100,
  ease: linear
})

animate({
  to: ["#fff", "#000", "#f00"],
  ease: [linear, easeInOut]
})

If set as any array, the length of this array must be one shorter than the number of values being animated between.

This is an array of values between 0 and 1 that defines at which point throughout the animation each keyframe should be reached.

This array should be the same length as the number of defined keyframes.

animate({
  to: ["#fff", "#000", "#f00"],
  offset: [0, 0.2, 1]
})

Springs are great for creating natural-feeling interfaces and dynamic interruptable animations.

A spring animation will be used if any of the stiffness, damping or mass options are detected.

Note: A spring simulation is inherently numerical so if it's given a color, array or object, it runs the animation from 0 to 100 and interpolates that to the given values. This strategy is likely to be tweaked before the official release so animations made this way may change in feel.

A single value to animate to.

animate({
  to: 100,
  type: "spring"
})

If to is an array, any defined from will be ignored.

This defines the stiffness of the spring. A higher stiffness will result in a snappier animation.

Defaults to 100

animate({
  to: 100,
  stiffness: 1000
})

This is the opposing force to stiffness. As you reduce this value, relative to stiffness, the spring will become bouncier and the animation will last longer. Likewise, higher relative values will have less bounciness and result in shorter animations.

Defaults to 10

animate({
  to: 100,
  damping: 50
})

This is the mass of the animating object. Heavier objects will take longer to speed up and slow down.

Defaults to 1.

animate({
  to: 100,
  mass: 2
})

The initial velocity, in units per second, of the animation.

animate({
  to: 100,
  velocity: 1000
})

The duration of the spring, in milliseconds.

Will be overridden by stiffness, mass or damping.

animate({
  to: 100,
  duration: 1000
})

The bounciness of the spring, as a value between 0 and 1, where 0 is no bounce.

Will be overridden by stiffness, mass or damping.

animate({
  to: 100,
  bounce: 0.2
})

The distance from the animation target at which the animation can be considered complete. When both restDelta and restSpeed are met, the animation completes.

animate({
  to: 100,
  restDelta: 0.5
})

The absolute velocity, in units per second, below which the animation can be considered complete. When both restDelta and restSpeed are met, the animation completes. Defaults to 10.

animate({
  to: 100,
  restSpeed: 5
})

animate returns PlaybackControls, which can be used to control the playback of the animation.

Currently this only includes a stop method, but may expand with more.

Stops the animation.

const playback = animate({ from: 0, to: 100 })
playback.stop()

The inertia animation is used to gradually decelerate a number. Think smartphone scroll momentum.

In addition to animate's from, onUpdate and onComplete options, inertia also supports the following:

The initial velocity, in units per second, of the animation.

inertia({
  from: 0,
  velocity: 100
})

A constant with which to calculate a target value. Higher power = further target.

Defaults to 0.8.

inertia({
  from: 0,
  power: 0.3
})

Adjusting the time constant will change the duration of the deceleration, thereby affecting its feel.

Defaults to 350.

inertia({
  from: 0,
  velocity: 100,
  timeConstant: 400
})

A function that receives the calculated target and returns a new one. Useful for snapping the target to a grid.

const roundToNearest = target => v => Math.ceil(v / target) * target

inertia({
  from: 0,
  velocity: 100,
  modifyTarget: roundToNearest(100)
})

The minimum value at which the animation will switch from gradual deceleration and use a spring animation to snap to this point.

inertia({
  from: 50,
  velocity: -100,
  min: 0
})

The maximum value at which the animation will switch from gradual deceleration and use a spring animation to snap to this point.

inertia({
  from: 50,
  velocity: 100,
  max: 100
})

This defines the stiffness of the spring when the animation hits either min or max. A higher stiffness will result in a snappier animation.

Defaults to 500

inertia({
  from: 0,
  velocity: 100,
  max: 50,
  bounceStiffness: 1000
})

This is the opposing force to bounceStiffness. As you reduce this value, relative to bounceStiffness, the spring will become bouncier and the animation will last longer. Likewise, higher relative values will have less bounciness and result in shorter animations.

Defaults to 10

inertia({
  from: 0,
  velocity: 100,
  max: 50,
  bounceDamping: 300
})

The distance from the animation target at which the animation can be considered complete.

inertia({
  from: 0,
  velocity: 100,
  restDelta: 0.5
})

Powering animate and inertia are the keyframes, spring, and decay iterators.

import { keyframes, spring, decay } from "popmotion";

Iterators give you the ability to run an animation with a high degree of control. For example, Framer uses the spring iterator to draw its animation editor visualiser by running it synchronously.

Each can be initialised with the matching options above (decay with a subset of inertia's options, excluding the bounce- options):

const animation = spring({
  from: 0,
  to: 100,
  stiffness: 200
})

With the returned iterator, you can resolve the animation at a specific timestamp with its next method.

// Resolve the animation at 200ms
const { value, done } = animation.next(200)

Popmotion includes a number of in-built easing functions, as well as factory functions to make entirely new ones.

Each easing function can be imported like so:

import { linear } from "popmotion"

Each function accepts a progress value between 0 and 1, and returns a new one:

const progress = 0.5
const easedProgress = easeInOut(progress)

• linear
• easeIn
• easeInOut
• easeOut
• circIn
• circInOut
• circOut
• backIn
• backInOut
• backOut
• anticipate
• bounceIn
• bounceInOut
• bounceOut

import { cubicBezier } from "popmotion"

const easing = cubicBezier(0, .42, 0, 1)

New cubic bezier definitions can be created in the Framer animation editor and copy/pasted directly into this function.

steps returns an easing function that will convert the animation into a discrete series of steps.

import { steps } from "popmotion"

const easing = steps(5)

It optionally accepts a second parameter, either "start" or "end" (default)that decides whether the steps are aligned with the start or end of the animation.

steps(5, "start")

Mirrors an existing easing function.

Reverses an existing easing function. For instance, providing it easeIn would return an easeOut.

import { reverseEasing, linear } from "popmotion"

const reversed = reverseEasing(linear)
reversed(1) // 0
reversed(0.5) // 0.5
reversed(0) // 1

Creates an easing function based on the exponent of the provided power. The higher the power, the stronger the easing.

import { createExpoIn } from "popmotion"

const expoIn = createExpoIn(4)

The returned easing function is an ease in, which means it starts slow and finished fast. mirrorEasing and reverseEasing can be used to create ease in out, and ease out variations:

const expoIn = createExpoIn(4)
const expoOut = mirrorEasing(easeIn)
const expoInOut = reverseEasing(easeIn)

Creates an easing function with an overshoot. It accepts a power value, the higher the power the stronger the overshoot.

import { createBackIn } from "popmotion"

const backIn = createBackIn(4)

The returned easing function is an ease in, which means the overshoot happens at the start of the animation. mirrorEasing and reverseEasing can be used to create ease in out, and ease out variations:

const backIn = createBackIn(4)
const backOut = mirrorEasing(easeIn)
const backInOut = reverseEasing(easeIn)

Creates an easing that pulls back a little before animating out with an overshoot. The stronger the power the bigger the overshoot.

import { createAnticipate } from "popmotion"

const anticipate = createAnticipate(4)

Returns an angle between two points, in degrees.

import { angle } from "popmotion"

angle(
  { x: 0, y: 0 },
  { x: 45, y: 100 }
)

import { attract } from "popmotion"

attract(5, 10, 12)

import { attractExpo } from "popmotion"

attractExpo(5, 10, 12)

Clamp a value to within the given range.

import { clamp } from "popmotion"

const min = 50
const max = 100
clamp(min, max, 150) // 100

Converts degrees to radians.

import { degreesToRadians } from "popmotion"

degreesToRadians(45) // 0.785...

Returns the distance between two numbers, two 2D points, or two 3D points.

import { distance } from "popmotion"

distance(10, 50)
distance({ x: 0, y: 0 }, { x: 45, y: 100 })
distance({ x: 0, y: 0, z: 100 }, { x: 45, y: 100, z: 0 })

Creates a function that will interpolate from an linear series of numbers, to a non-linear series of numbers, strings of the same numerical format, colours, or arrays/objects of those.

import { interpolate } from "popmotion"

const mapXToOpacity = interpolate(
  [-100, 0, 100],
  [0, 1, 0]
)
mapXToOpacity(-50) // 0.5

const mapProgressToValues = interpolate(
  [0, 1],
  [
    { x: 0, color: "#fff" },
    { x: 100, color: "#000" }
  ]
)
mapProgressToValues(0.5) // { x: 50, color: "#888" }

const rescale = interpolate(
  [0, 1],
  [100, 200],
  { clamp: false }
)
rescale(2) // 300

interpolate accepts an optional third argument, an object of options.

• clamp: Clamps values to within given range. Defaults to true.
• ease: An Easing function, or array of easing functions, to ease the interpolation of each segment.
• mixer: A function that, when provided a from and to value, will return a new function that accepts a progress value between 0 and 1 to mix between those two values. For integration with libraries like Flubber.

Returns true if the provided argument is a 2D point.

import { isPoint } from "popmotion"

isPoint({ x: 0 }) // false
isPoint({ x: 0, y: 0 }) // true

Returns true if the provided argument is a 3D point.

import { isPoint3D } from "popmotion"

isPoint3D({ x: 0 }) // false
isPoint3D({ x: 0, y: 0 }) // false
isPoint3D({ x: 0, y: 0, z: 0 }) // true

Will mix between two values, given progress as a third argument.

import { mix } from "popmotion"

mix(0, 100, 0.5) // 50
mix(0, 100, 2) // 200

Returns a function that, when provided a progress value, will mix between two colors. Accepts hex, rgba and hsla colors.

import { mixColor } from "popmotion"

mixColor("#000", "#fff")(0.5) // "rgba(125, 125, 125, 1)"

Returns a function that, when provided a progress value, will mix between two strings with the same order of numbers and colors.

import { mixComplex } from "popmotion"

mixComplex("100px #fff", "0px #000")(0.5) // "50px rgba(125, 125, 125, 1)"

Given a point, angle in degrees, and distance, will return a new point.

import { pointFromVector } from "popmotion"

const point = { x: 0, y: 0 }
const angle = 45
const distance = 100

pointFromVector(point, angle, distance)

Given a min and a max range, and a value, will return the progress of the value within the range as normalised to a 0-1 range.

import { progress } from "popmotion"

const min = 100
const max = 200
progress(min, max, 150) // 0.5

Converts radians to degrees.

import { radiansToDegrees } from "popmotion"

radiansToDegrees(0.785) // 45

Creates a function that will snap numbers to the nearest in a provided array or to a regular interval.

import { snap } from "popmotion"

// Snap to regular intervals
const snapTo = snap(45);

snapTo(1); // 0
snapTo(40); // 45
snapTo(50); // 45
snapTo(80); // 90

// Snap to values in an array
const snapTo = snap([-100, -50, 100, 200]);

snapTo(-200); // -100
snapTo(-76); // -100
snapTo(-74); // -50

Rounds a number to a specific decimal place.

import { toDecimal } from "popmotion"

toDecimal(3.3333); // 3.33
toDecimal(6.6666, 1); // 6.67

import { velocityPerFrame } from "popmotion"

velocityPerFrame(50, 16.7); // 0.835

import { velocityPerSecond } from "popmotion"

velocityPerSecond(1, 16.7); // 59.880...

import { wrap } from "popmotion"

wrap(0, 1, 0.5); // 0.5
wrap(0, 1, 1.5); // 0.5