jstweening

jstweening is a lightweight JavaScript library providing a wide range of easing functions for animations and interpolations. It includes classic polynomial, trigonometric, exponential, circular, elastic, back, and bounce easing curves – with both ease-in, ease-out, and ease-in-out variants.

All easing functions operate over a normalized time parameter t ∈ [0, 1].

📦 Installation

npm install jstweening

🔧 Usage

import { easeInOutCubic } from "jstweening";

const t = 0.35;
const eased = easeInOutCubic(t);

Or with CommonJS:

const { easeInOutCubic } = require("jstweening");

📘 API Reference

Each easing function takes a normalized t between 0 and 1, and returns a transformed value within the same range.

Basic

linear(t: number): number

Polynomial

easeInQuad(t: number): number
easeOutQuad(t: number): number
easeInOutQuad(t: number): number

easeInCubic(t: number): number
easeOutCubic(t: number): number
easeInOutCubic(t: number): number

easeInQuart(t: number): number
easeOutQuart(t: number): number
easeInOutQuart(t: number): number

easeInQuint(t: number): number
easeOutQuint(t: number): number
easeInOutQuint(t: number): number

easeInPoly(t: number, degree: number): number
easeOutPoly(t: number, degree: number): number
easeInOutPoly(t: number, degree: number): number

Trigonometric

easeInSine(t: number): number
easeOutSine(t: number): number
easeInOutSine(t: number): number

Exponential

easeInExpo(t: number): number
easeOutExpo(t: number): number
easeInOutExpo(t: number): number

Circular

easeInCirc(t: number): number
easeOutCirc(t: number): number
easeInOutCirc(t: number): number

Elastic

easeInElastic(t: number, amplitude?: number, period?: number): number
easeOutElastic(t: number, amplitude?: number, period?: number): number
easeInOutElastic(t: number, amplitude?: number, period?: number): number

Back

easeInBack(t: number, s?: number): number
easeOutBack(t: number, s?: number): number
easeInOutBack(t: number, s?: number): number

Bounce

easeInBounce(t: number): number
easeOutBounce(t: number): number
easeInOutBounce(t: number): number

🧪 Example

import { easeOutBounce } from "jstweening";

for (let i = 0; i <= 10; i++) {
    const t = i / 10;
    console.log(`t=${t.toFixed(1)} → ${easeOutBounce(t).toFixed(3)}`);
}

📝 License

MIT © 2025 Oğuzhan Umutlu