src/ease/index.js

import { PI } from '../constants';

/**
 * The Ease class provides a collection of easing functions for use with System
 */
export const ease = {
  easeLinear: function(value) {
    return value;
  },

  easeInQuad: function(value) {
    return Math.pow(value, 2);
  },

  easeOutQuad: function(value) {
    return -(Math.pow(value - 1, 2) - 1);
  },

  easeInOutQuad: function(value) {
    if ((value /= 0.5) < 1) return 0.5 * Math.pow(value, 2);

    return -0.5 * ((value -= 2) * value - 2);
  },

  easeInCubic: function(value) {
    return Math.pow(value, 3);
  },

  easeOutCubic: function(value) {
    return Math.pow(value - 1, 3) + 1;
  },

  easeInOutCubic: function(value) {
    if ((value /= 0.5) < 1) return 0.5 * Math.pow(value, 3);

    return 0.5 * (Math.pow(value - 2, 3) + 2);
  },

  easeInQuart: function(value) {
    return Math.pow(value, 4);
  },

  easeOutQuart: function(value) {
    return -(Math.pow(value - 1, 4) - 1);
  },

  easeInOutQuart: function(value) {
    if ((value /= 0.5) < 1) return 0.5 * Math.pow(value, 4);

    return -0.5 * ((value -= 2) * Math.pow(value, 3) - 2);
  },

  easeInSine: function(value) {
    return -Math.cos(value * (PI / 2)) + 1;
  },

  easeOutSine: function(value) {
    return Math.sin(value * (PI / 2));
  },

  easeInOutSine: function(value) {
    return -0.5 * (Math.cos(PI * value) - 1);
  },

  easeInExpo: function(value) {
    return value === 0 ? 0 : Math.pow(2, 10 * (value - 1));
  },

  easeOutExpo: function(value) {
    return value === 1 ? 1 : -Math.pow(2, -10 * value) + 1;
  },

  easeInOutExpo: function(value) {
    if (value === 0) return 0;
    if (value === 1) return 1;
    if ((value /= 0.5) < 1) return 0.5 * Math.pow(2, 10 * (value - 1));

    return 0.5 * (-Math.pow(2, -10 * --value) + 2);
  },

  easeInCirc: function(value) {
    return -(Math.sqrt(1 - value * value) - 1);
  },

  easeOutCirc: function(value) {
    return Math.sqrt(1 - Math.pow(value - 1, 2));
  },

  easeInOutCirc: function(value) {
    if ((value /= 0.5) < 1) return -0.5 * (Math.sqrt(1 - value * value) - 1);

    return 0.5 * (Math.sqrt(1 - (value -= 2) * value) + 1);
  },

  easeInBack: function(value) {
    var s = 1.70158;

    return value * value * ((s + 1) * value - s);
  },

  easeOutBack: function(value) {
    var s = 1.70158;

    return (value = value - 1) * value * ((s + 1) * value + s) + 1;
  },

  easeInOutBack: function(value) {
    var s = 1.70158;

    if ((value /= 0.5) < 1)
      return 0.5 * (value * value * (((s *= 1.525) + 1) * value - s));

    return 0.5 * ((value -= 2) * value * (((s *= 1.525) + 1) * value + s) + 2);
  }
};

export const {
  easeLinear,
  easeInQuad,
  easeOutQuad,
  easeInOutQuad,
  easeInCubic,
  easeOutCubic,
  easeInOutCubic,
  easeInQuart,
  easeOutQuart,
  easeInOutQuart,
  easeInSine,
  easeOutSine,
  easeInOutSine,
  easeInExpo,
  easeOutExpo,
  easeInOutExpo,
  easeInCirc,
  easeOutCirc,
  easeInOutCirc,
  easeInBack,
  easeOutBack,
  easeInOutBack
} = ease;

export const setEasingByName = easeName => {
  if (ease[easeName]) return ease[easeName];
  else return ease.easeLinear;
};

export const getEasingByName = name =>
  ease[name] ? ease[name] : ease.easeLinear;