d3-ease

Easing is a method of distorting time to control apparent motion in animation. It is most commonly used for slow-in, slow-out. By easing time, animated transitions are smoother and exhibit more plausible motion.

The easing types in this module implement the ease method, which takes a normalized time t and returns the corresponding “eased” time tʹ. Both the normalized time and the eased time are typically in the range [0,1], where 0 represents the start of the animation and 1 represents the end; some easing types, such as elastic, may return eased times slightly outside this range. A good easing type should return 0 if t = 0 and 1 if t = 1. See the easing explorer for a visual demonstration.

These easing types are largely based on work by Robert Penner.

Installing

If you use npm, npm install d3-ease. You can also download the latest release on GitHub. For vanilla HTML in modern browsers, import d3-ease from Skypack:

<script type="module">

import {easeCubic} from "https://cdn.skypack.dev/d3-ease@3";

const e = easeCubic(0.25);

</script>

For legacy environments, you can load d3-ease’s UMD bundle from an npm-based CDN such as jsDelivr; a d3 global is exported:

<script src="https://cdn.jsdelivr.net/npm/d3-ease@3"></script>
<script>

const e = d3.easeCubic(0.25);

</script>

Try d3-ease in your browser.

API Reference

# ease(t)

Given the specified normalized time t, typically in the range [0,1], returns the “eased” time tʹ, also typically in [0,1]. 0 represents the start of the animation and 1 represents the end. A good implementation returns 0 if t = 0 and 1 if t = 1. See the easing explorer for a visual demonstration. For example, to apply cubic easing:

const te = d3.easeCubic(t);

Similarly, to apply custom elastic easing:

// Before the animation starts, create your easing function.
const customElastic = d3.easeElastic.period(0.4);

// During the animation, apply the easing function.
const te = customElastic(t);

# d3.easeLinear(t) <>

Linear easing; the identity function; linear(t) returns t.

# d3.easePolyIn(t) <>

Polynomial easing; raises t to the specified exponent. If the exponent is not specified, it defaults to 3, equivalent to cubicIn.

# d3.easePolyOut(t) <>

Reverse polynomial easing; equivalent to 1 - polyIn(1 - t). If the exponent is not specified, it defaults to 3, equivalent to cubicOut.

# d3.easePoly(t) <>
# d3.easePolyInOut(t) <>

Symmetric polynomial easing; scales polyIn for t in [0, 0.5] and polyOut for t in [0.5, 1]. If the exponent is not specified, it defaults to 3, equivalent to cubic.

# poly.exponent(e) <>

Returns a new polynomial easing with the specified exponent e. For example, to create equivalents of linear, quad, and cubic:

const linear = d3.easePoly.exponent(1);
const quad = d3.easePoly.exponent(2);
const cubic = d3.easePoly.exponent(3);

# d3.easeQuadIn(t) <>

Quadratic easing; equivalent to polyIn.exponent(2).

# d3.easeQuadOut(t) <>

Reverse quadratic easing; equivalent to 1 - quadIn(1 - t). Also equivalent to polyOut.exponent(2).

# d3.easeQuad(t) <>
# d3.easeQuadInOut(t) <>

Symmetric quadratic easing; scales quadIn for t in [0, 0.5] and quadOut for t in [0.5, 1]. Also equivalent to poly.exponent(2).

# d3.easeCubicIn(t) <>

Cubic easing; equivalent to polyIn.exponent(3).

# d3.easeCubicOut(t) <>

Reverse cubic easing; equivalent to 1 - cubicIn(1 - t). Also equivalent to polyOut.exponent(3).

# d3.easeCubic(t) <>
# d3.easeCubicInOut(t) <>

Symmetric cubic easing; scales cubicIn for t in [0, 0.5] and cubicOut for t in [0.5, 1]. Also equivalent to poly.exponent(3).

# d3.easeSinIn(t) <>

Sinusoidal easing; returns sin(t).

# d3.easeSinOut(t) <>

Reverse sinusoidal easing; equivalent to 1 - sinIn(1 - t).

# d3.easeSin(t) <>
# d3.easeSinInOut(t) <>

Symmetric sinusoidal easing; scales sinIn for t in [0, 0.5] and sinOut for t in [0.5, 1].

# d3.easeExpIn(t) <>

Exponential easing; raises 2 to the exponent 10 * (t - 1).

# d3.easeExpOut(t) <>

Reverse exponential easing; equivalent to 1 - expIn(1 - t).

# d3.easeExp(t) <>
# d3.easeExpInOut(t) <>

Symmetric exponential easing; scales expIn for t in [0, 0.5] and expOut for t in [0.5, 1].

# d3.easeCircleIn(t) <>

Circular easing.

# d3.easeCircleOut(t) <>

Reverse circular easing; equivalent to 1 - circleIn(1 - t).

# d3.easeCircle(t) <>
# d3.easeCircleInOut(t) <>

Symmetric circular easing; scales circleIn for t in [0, 0.5] and circleOut for t in [0.5, 1].

# d3.easeElasticIn(t) <>

Elastic easing, like a rubber band. The amplitude and period of the oscillation are configurable; if not specified, they default to 1 and 0.3, respectively.

# d3.easeElastic(t) <>
# d3.easeElasticOut(t) <>

Reverse elastic easing; equivalent to 1 - elasticIn(1 - t).

# d3.easeElasticInOut(t) <>

Symmetric elastic easing; scales elasticIn for t in [0, 0.5] and elasticOut for t in [0.5, 1].

# elastic.amplitude(a) <>

Returns a new elastic easing with the specified amplitude a.

# elastic.period(p) <>

Returns a new elastic easing with the specified period p.

# d3.easeBackIn(t) <>

Anticipatory easing, like a dancer bending his knees before jumping off the floor. The degree of overshoot is configurable; if not specified, it defaults to 1.70158.