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BezierEasing provides Cubic Bezier Curve easing which generalizes easing functions (ease-in, ease-out, ease-in-out, ...any other custom curve) exactly like in CSS Transitions.

Implementing efficient lookup is not easy because it implies projecting the X coordinate to a Bezier Curve. This micro library uses fast heuristics (involving dichotomic search, newton-raphson, sampling) to focus on performance and precision.

It is heavily based on implementations available in Firefox and Chrome (for the CSS transition-timing-function property).


var easing = BezierEasing(0, 0, 1, 0.5);
// easing allows to project x in [0.0,1.0] range onto the bezier-curve defined by the 4 points (see schema below).
console.log(easing(0.0)); // 0.0
console.log(easing(0.5)); // 0.3125
console.log(easing(1.0)); // 1.0

(this schema is from the CSS spec)


BezierEasing(P1.x, P1.y, P2.x, P2.y)


npm install bezier-easing

It is the equivalent to CSS Transitions' transition-timing-function.

In the same way you can define in CSS cubic-bezier(0.42, 0, 0.58, 1), with BezierEasing, you can define it using BezierEasing(0.42, 0, 0.58, 1) which have the `` function taking an X and computing the Y interpolated easing value (see schema).


MIT License.


Build Status

npm test

See also

Who use it?

More informations

Implementation based on this article.


You need a node installed.

Install the deps:

npm install

The library is in index.js.

Ensure any modication will:

  • keep validating the tests (run npm test)
  • not bring performance regression (compare with npm run benchmark – don't rely 100% on its precision but it still helps to notice big gaps)
  • Run the visual example: npm run visual


cubic-bezier implementation for your JavaScript animation easings – MIT License





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