text: // Defaults
  
  const defaultInstanceSettings = {
    update: null,
    begin: null,
    loopBegin: null,
    changeBegin: null,
    change: null,
    changeComplete: null,
    loopComplete: null,
    complete: null,
    loop: 1,
    direction: 'normal',
    autoplay: true,
    timelineOffset: 0
  }
  
  const defaultTweenSettings = {
    duration: 1000,
    delay: 0,
    endDelay: 0,
    easing: 'easeOutElastic(1, .5)',
    round: 0
  }
  
  const validTransforms = ['translateX', 'translateY', 'translateZ', 'rotate', 'rotateX', 'rotateY', 'rotateZ', 'scale', 'scaleX', 'scaleY', 'scaleZ', 'skew', 'skewX', 'skewY', 'perspective', 'matrix', 'matrix3d'];
  
  // Caching
  
  const cache = {
    CSS: {},
    springs: {}
  }
  
  // Utils
  
  function minMax(val, min, max) {
    return Math.min(Math.max(val, min), max);
  }
  
  function stringContains(str, text) {
    return str.indexOf(text) > -1;
  }
  
  function applyArguments(func, args) {
    return func.apply(null, args);
  }
  
  const is = {
    arr: a => Array.isArray(a),
    obj: a => stringContains(Object.prototype.toString.call(a), 'Object'),
    pth: a => is.obj(a) && a.hasOwnProperty('totalLength'),
    svg: a => a instanceof SVGElement,
    inp: a => a instanceof HTMLInputElement,
    dom: a => a.nodeType || is.svg(a),
    str: a => typeof a === 'string',
    fnc: a => typeof a === 'function',
    und: a => typeof a === 'undefined',
    nil: a => is.und(a) || a === null,
    hex: a => /(^#[0-9A-F]{6}$)|(^#[0-9A-F]{3}$)/i.test(a),
    rgb: a => /^rgb/.test(a),
    hsl: a => /^hsl/.test(a),
    col: a => (is.hex(a) || is.rgb(a) || is.hsl(a)),
    key: a => !defaultInstanceSettings.hasOwnProperty(a) && !defaultTweenSettings.hasOwnProperty(a) && a !== 'targets' && a !== 'keyframes',
  }
  
  // Easings
  
  function parseEasingParameters(string) {
    const match = /\(([^)]+)\)/.exec(string);
    return match ? match[1].split(',').map(p => parseFloat(p)) : [];
  }
  
  // Spring solver inspired by Webkit Copyright © 2016 Apple Inc. All rights reserved. https://webkit.org/demos/spring/spring.js
  
  function spring(string, duration) {
  
    const params = parseEasingParameters(string);
    const mass = is.und(params[0]) ? 1 : minMax(params[0], .1, 100);
    const stiffness = is.und(params[1]) ? 100 : minMax(params[1], .1, 100);
    const damping = is.und(params[2]) ? 10 : minMax(params[2], .1, 100);
    const velocity = is.und(params[3]) ? .1 : minMax(params[3], .1, 100);
    const w0 = Math.sqrt(stiffness / mass);
    const zeta = damping / (2 * Math.sqrt(stiffness * mass));
    const wd = zeta < 1 ? w0 * Math.sqrt(1 - zeta * zeta) : 0;
    const a = 1;
    const b = zeta < 1 ? (zeta * w0 + -velocity) / wd : -velocity + w0;
  
    function solver(t) {
      let progress = duration ? (duration * t) / 1000 : t;
      if (zeta < 1) {
        progress = Math.exp(-progress * zeta * w0) * (a * Math.cos(wd * progress) + b * Math.sin(wd * progress));
      } else {
        progress = (a + b * progress) * Math.exp(-progress * w0);
      }
      return (t === 0 || t === 1) ? t : 1 - progress;
    }
  
    function getDuration() {
      const cached = cache.springs[string];
      if (cached) return cached;
      const frame = 1/6;
      let elapsed = 0;
      let rest = 0;
      while(true) {
        elapsed += frame;
        if (solver(elapsed) === 1) {
          rest++;
          if (rest >= 16) break;
        } else {
          rest = 0;
        }
      }
      const duration = elapsed * frame * 1000;
      cache.springs[string] = duration;
      return duration;
    }
  
    return duration ? solver : getDuration;
  
  }
  
  // Basic steps easing implementation https://developer.mozilla.org/fr/docs/Web/CSS/transition-timing-function
  
  function steps(steps = 10) {
    return t => Math.ceil((minMax(t, 0.000001, 1)) * steps) * (1 / steps);
  }
  
  // BezierEasing https://github.com/gre/bezier-easing
  
  const bezier = (() => {
  
    const kSplineTableSize = 11;
    const kSampleStepSize = 1.0 / (kSplineTableSize - 1.0);
  
    function A(aA1, aA2) { return 1.0 - 3.0 * aA2 + 3.0 * aA1 };
    function B(aA1, aA2) { return 3.0 * aA2 - 6.0 * aA1 };
    function C(aA1)      { return 3.0 * aA1 };
  
    function calcBezier(aT, aA1, aA2) { return ((A(aA1, aA2) * aT + B(aA1, aA2)) * aT + C(aA1)) * aT };
    function getSlope(aT, aA1, aA2) { return 3.0 * A(aA1, aA2) * aT * aT + 2.0 * B(aA1, aA2) * aT + C(aA1) };
  
    function binarySubdivide(aX, aA, aB, mX1, mX2) {
      let currentX, currentT, i = 0;
      do {
        currentT = aA + (aB - aA) / 2.0;
        currentX = calcBezier(currentT, mX1, mX2) - aX;
        if (currentX > 0.0) { aB = currentT } else { aA = currentT };
      } while (Math.abs(currentX) > 0.0000001 && ++i < 10);
      return currentT;
    }
  
    function newtonRaphsonIterate(aX, aGuessT, mX1, mX2) {
      for (let i = 0; i < 4; ++i) {
        const currentSlope = getSlope(aGuessT, mX1, mX2);
        if (currentSlope === 0.0) return aGuessT;
        const currentX = calcBezier(aGuessT, mX1, mX2) - aX;
        aGuessT -= currentX / currentSlope;
      }
      return aGuessT;
    }
  
    function bezier(mX1, mY1, mX2, mY2) {
  
      if (!(0 <= mX1 && mX1 <= 1 && 0 <= mX2 && mX2 <= 1)) return;
      let sampleValues = new Float32Array(kSplineTableSize);
  
      if (mX1 !== mY1 || mX2 !== mY2) {
        for (let i = 0; i < kSplineTableSize; ++i) {
          sampleValues[i] = calcBezier(i * kSampleStepSize, mX1, mX2);
        }
      }
  
      function getTForX(aX) {
  
        let intervalStart = 0;
        let currentSample = 1;
        const lastSample = kSplineTableSize - 1;
  
        for (; currentSample !== lastSample && sampleValues[currentSample] <= aX; ++currentSample) {
          intervalStart += kSampleStepSize;
        }
  
        --currentSample;
  
        const dist = (aX - sampleValues[currentSample]) / (sampleValues[currentSample + 1] - sampleValues[currentSample]);
        const guessForT = intervalStart + dist * kSampleStepSize;
        const initialSlope = getSlope(guessForT, mX1, mX2);
  
        if (initialSlope >= 0.001) {
          return newtonRaphsonIterate(aX, guessForT, mX1, mX2);
        } else if (initialSlope === 0.0) {
          return guessForT;
        } else {
          return binarySubdivide(aX, intervalStart, intervalStart + kSampleStepSize, mX1, mX2);
        }
  
      }
  
      return x => {
        if (mX1 === mY1 && mX2 === mY2) return x;
        if (x === 0 || x === 1) return x;
        return calcBezier(getTForX(x), mY1, mY2);
      }
  
    }
  
    return bezier;
  
  })();
  
  const penner = (() => {
  
    // Based on jQuery UI's implemenation of easing equations from Robert Penner (http://www.robertpenner.com/easing)
  
    const eases = { linear: () => t => t };
  
    const functionEasings = {
      Sine: () => t => 1 - Math.cos(t * Math.PI / 2),
      Circ: () => t => 1 - Math.sqrt(1 - t * t),
      Back: () => t => t * t * (3 * t - 2),
      Bounce: () => t => {
        let pow2, b = 4;
        while (t < (( pow2 = Math.pow(2, --b)) - 1) / 11) {};
        return 1 / Math.pow(4, 3 - b) - 7.5625 * Math.pow(( pow2 * 3 - 2 ) / 22 - t, 2)
      },
      Elastic: (amplitude = 1, period = .5) => {
        const a = minMax(amplitude, 1, 10);
        const p = minMax(period, .1, 2);
        return t => {
          return (t === 0 || t === 1) ? t : 
            -a * Math.pow(2, 10 * (t - 1)) * Math.sin((((t - 1) - (p / (Math.PI * 2) * Math.asin(1 / a))) * (Math.PI * 2)) / p);
        }
      }
    }
  
    const baseEasings = ['Quad', 'Cubic', 'Quart', 'Quint', 'Expo'];
  
    baseEasings.forEach((name, i) => {
      functionEasings[name] = () => t => Math.pow(t, i + 2);
    });
  
    Object.keys(functionEasings).forEach(name => {
      const easeIn = functionEasings[name];
      eases['easeIn' + name] = easeIn;
      eases['easeOut' + name] = (a, b) => t => 1 - easeIn(a, b)(1 - t);
      eases['easeInOut' + name] = (a, b) => t => t < 0.5 ? easeIn(a, b)(t * 2) / 2 : 
        1 - easeIn(a, b)(t * -2 + 2) / 2;
      eases['easeOutIn' + name] = (a, b) => t => t < 0.5 ? (1 - easeIn(a, b)(1 - t * 2)) / 2 : 
        (easeIn(a, b)(t * 2 - 1) + 1) / 2;
    });
  
    return eases;
  
  })();
  
  function parseEasings(easing, duration) {
    if (is.fnc(easing)) return easing;
    const name = easing.split('(')[0];
    const ease = penner[name];
    const args = parseEasingParameters(easing);
    switch (name) {
      case 'spring' : return spring(easing, duration);
      case 'cubicBezier' : return applyArguments(bezier, args);
      case 'steps' : return applyArguments(steps, args);
      default : return applyArguments(ease, args);
    }
  }
  
  // Strings
  
  function selectString(str) {
    try {
      let nodes = document.querySelectorAll(str);
      return nodes;
    } catch(e) {
      return;
    }
  }
  
  // Arrays
  
  function filterArray(arr, callback) {
    const len = arr.length;
    const thisArg = arguments.length >= 2 ? arguments[1] : void 0;
    const result = [];
    for (let i = 0; i < len; i++) {
      if (i in arr) {
        const val = arr[i];
        if (callback.call(thisArg, val, i, arr)) {
          result.push(val);
        }
      }
    }
    return result;
  }
  
  function flattenArray(arr) {
    return arr.reduce((a, b) => a.concat(is.arr(b) ? flattenArray(b) : b), []);
  }
  
  function toArray(o) {
    if (is.arr(o)) return o;
    if (is.str(o)) o = selectString(o) || o;
    if (o instanceof NodeList || o instanceof HTMLCollection) return [].slice.call(o);
    return [o];
  }
  
  function arrayContains(arr, val) {
    return arr.some(a => a === val);
  }
  
  // Objects
  
  function cloneObject(o) {
    const clone = {};
    for (let p in o) clone[p] = o[p];
    return clone;
  }
  
  function replaceObjectProps(o1, o2) {
    const o = cloneObject(o1);
    for (let p in o1) o[p] = o2.hasOwnProperty(p) ? o2[p] : o1[p];
    return o;
  }
  
  function mergeObjects(o1, o2) {
    const o = cloneObject(o1);
    for (let p in o2) o[p] = is.und(o1[p]) ? o2[p] : o1[p];
    return o;
  }
  
  // Colors
  
  function rgbToRgba(rgbValue) {
    const rgb = /rgb\((\d+,\s*[\d]+,\s*[\d]+)\)/g.exec(rgbValue);
    return rgb ? `rgba(${rgb[1]},1)` : rgbValue;
  }
  
  function hexToRgba(hexValue) {
    const rgx = /^#?([a-f\d])([a-f\d])([a-f\d])$/i;
    const hex = hexValue.replace(rgx, (m, r, g, b) => r + r + g + g + b + b );
    const rgb = /^#?([a-f\d]{2})([a-f\d]{2})([a-f\d]{2})$/i.exec(hex);
    const r = parseInt(rgb[1], 16);
    const g = parseInt(rgb[2], 16);
    const b = parseInt(rgb[3], 16);
    return `rgba(${r},${g},${b},1)`;
  }
  
  function hslToRgba(hslValue) {
    const hsl = /hsl\((\d+),\s*([\d.]+)%,\s*([\d.]+)%\)/g.exec(hslValue) || /hsla\((\d+),\s*([\d.]+)%,\s*([\d.]+)%,\s*([\d.]+)\)/g.exec(hslValue);
    const h = parseInt(hsl[1], 10) / 360;
    const s = parseInt(hsl[2], 10) / 100;
    const l = parseInt(hsl[3], 10) / 100;
    const a = hsl[4] || 1;
    function hue2rgb(p, q, t) {
      if (t < 0) t += 1;
      if (t > 1) t -= 1;
      if (t < 1/6) return p + (q - p) * 6 * t;
      if (t < 1/2) return q;
      if (t < 2/3) return p + (q - p) * (2/3 - t) * 6;
      return p;
    }
    let r, g, b;
    if (s == 0) {
      r = g = b = l;
    } else {
      const q = l < 0.5 ? l * (1 + s) : l + s - l * s;
      const p = 2 * l - q;
      r = hue2rgb(p, q, h + 1/3);
      g = hue2rgb(p, q, h);
      b = hue2rgb(p, q, h - 1/3);
    }
    return `rgba(${r * 255},${g * 255},${b * 255},${a})`;
  }
  
  function colorToRgb(val) {
    if (is.rgb(val)) return rgbToRgba(val);
    if (is.hex(val)) return hexToRgba(val);
    if (is.hsl(val)) return hslToRgba(val);
  }
  
  // Units
  
  function getUnit(val) {
    const split = /[+-]?\d*\.?\d+(?:\.\d+)?(?:[eE][+-]?\d+)?(%|px|pt|em|rem|in|cm|mm|ex|ch|pc|vw|vh|vmin|vmax|deg|rad|turn)?$/.exec(val);
    if (split) return split[1];
  }
  
  function getTransformUnit(propName) {
    if (stringContains(propName, 'translate') || propName === 'perspective') return 'px';
    if (stringContains(propName, 'rotate') || stringContains(propName, 'skew')) return 'deg';
  }
  
  // Values
  
  function getFunctionValue(val, animatable) {
    if (!is.fnc(val)) return val;
    return val(animatable.target, animatable.id, animatable.total);
  }
  
  function getAttribute(el, prop) {
    return el.getAttribute(prop);
  }
  
  function convertPxToUnit(el, value, unit) {
    const valueUnit = getUnit(value);
    if (arrayContains([unit, 'deg', 'rad', 'turn'], valueUnit)) return value;
    const cached = cache.CSS[value + unit];
    if (!is.und(cached)) return cached;
    const baseline = 100;
    const tempEl = document.createElement(el.tagName);
    const parentEl = (el.parentNode && (el.parentNode !== document)) ? el.parentNode : document.body;
    parentEl.appendChild(tempEl);
    tempEl.style.position = 'absolute';
    tempEl.style.width = baseline + unit;
    const factor = baseline / tempEl.offsetWidth;
    parentEl.removeChild(tempEl);
    const convertedUnit = factor * parseFloat(value);
    cache.CSS[value + unit] = convertedUnit;
    return convertedUnit;
  }
  
  function getCSSValue(el, prop, unit) {
    if (prop in el.style) {
      const uppercasePropName = prop.replace(/([a-z])([A-Z])/g, '$1-$2').toLowerCase();
      const value = el.style[prop] || getComputedStyle(el).getPropertyValue(uppercasePropName) || '0';
      return unit ? convertPxToUnit(el, value, unit) : value;
    }
  }
  
  function getAnimationType(el, prop) {
    if (is.dom(el) && !is.inp(el) && (!is.nil(getAttribute(el, prop)) || (is.svg(el) && el[prop]))) return 'attribute';
    if (is.dom(el) && arrayContains(validTransforms, prop)) return 'transform';
    if (is.dom(el) && (prop !== 'transform' && getCSSValue(el, prop))) return 'css';
    if (el[prop] != null) return 'object';
  }
  
  function getElementTransforms(el) {
    if (!is.dom(el)) return;
    const str = el.style.transform || '';
    const reg  = /(\w+)\(([^)]*)\)/g;
    const transforms = new Map();
    let m; while (m = reg.exec(str)) transforms.set(m[1], m[2]);
    return transforms;
  }
  
  function getTransformValue(el, propName, animatable, unit) {
    const defaultVal = stringContains(propName, 'scale') ? 1 : 0 + getTransformUnit(propName);
    const value = getElementTransforms(el).get(propName) || defaultVal;
    if (animatable) {
      animatable.transforms.list.set(propName, value);
      animatable.transforms['last'] = propName;
    }
    return unit ? convertPxToUnit(el, value, unit) : value;
  }
  
  function getOriginalTargetValue(target, propName, unit, animatable) {
    switch (getAnimationType(target, propName)) {
      case 'transform': return getTransformValue(target, propName, animatable, unit);
      case 'css': return getCSSValue(target, propName, unit);
      case 'attribute': return getAttribute(target, propName);
      default: return target[propName] || 0;
    }
  }
  
  function getRelativeValue(to, from) {
    const operator = /^(\*=|\+=|-=)/.exec(to);
    if (!operator) return to;
    const u = getUnit(to) || 0;
    const x = parseFloat(from);
    const y = parseFloat(to.replace(operator[0], ''));
    switch (operator[0][0]) {
      case '+': return x + y + u;
      case '-': return x - y + u;
      case '*': return x * y + u;
    }
  }
  
  function validateValue(val, unit) {
    if (is.col(val)) return colorToRgb(val);
    if (/\s/g.test(val)) return val;
    const originalUnit = getUnit(val);
    const unitLess = originalUnit ? val.substr(0, val.length - originalUnit.length) : val;
    if (unit) return unitLess + unit;
    return unitLess;
  }
  
  // getTotalLength() equivalent for circle, rect, polyline, polygon and line shapes
  // adapted from https://gist.github.com/SebLambla/3e0550c496c236709744
  
  function getDistance(p1, p2) {
    return Math.sqrt(Math.pow(p2.x - p1.x, 2) + Math.pow(p2.y - p1.y, 2));
  }
  
  function getCircleLength(el) {
    return Math.PI * 2 * getAttribute(el, 'r');
  }
  
  function getRectLength(el) {
    return (getAttribute(el, 'width') * 2) + (getAttribute(el, 'height') * 2);
  }
  
  function getLineLength(el) {
    return getDistance(
      {x: getAttribute(el, 'x1'), y: getAttribute(el, 'y1')}, 
      {x: getAttribute(el, 'x2'), y: getAttribute(el, 'y2')}
    );
  }
  
  function getPolylineLength(el) {
    const points = el.points;
    let totalLength = 0;
    let previousPos;
    for (let i = 0 ; i < points.numberOfItems; i++) {
      const currentPos = points.getItem(i);
      if (i > 0) totalLength += getDistance(previousPos, currentPos);
      previousPos = currentPos;
    }
    return totalLength;
  }
  
  function getPolygonLength(el) {
    const points = el.points;
    return getPolylineLength(el) + getDistance(points.getItem(points.numberOfItems - 1), points.getItem(0));
  }
  
  // Path animation
  
  function getTotalLength(el) {
    if (el.getTotalLength) return el.getTotalLength();
    switch(el.tagName.toLowerCase()) {
      case 'circle': return getCircleLength(el);
      case 'rect': return getRectLength(el);
      case 'line': return getLineLength(el);
      case 'polyline': return getPolylineLength(el);
      case 'polygon': return getPolygonLength(el);
    }
  }
  
  function setDashoffset(el) {
    const pathLength = getTotalLength(el);
    el.setAttribute('stroke-dasharray', pathLength);
    return pathLength;
  }
  
  // Motion path
  
  function getParentSvgEl(el) {
    let parentEl = el.parentNode;
    while (is.svg(parentEl)) {
      if (!is.svg(parentEl.parentNode)) break;
      parentEl = parentEl.parentNode;
    }
    return parentEl;
  }
  
  function getParentSvg(pathEl, svgData) {
    const svg = svgData || {};
    const parentSvgEl = svg.el || getParentSvgEl(pathEl);
    const rect = parentSvgEl.getBoundingClientRect();
    const viewBoxAttr = getAttribute(parentSvgEl, 'viewBox');
    const width = rect.width;
    const height = rect.height;
    const viewBox = svg.viewBox || (viewBoxAttr ? viewBoxAttr.split(' ') : [0, 0, width, height]);
    return {
      el: parentSvgEl,
      viewBox: viewBox,
      x: viewBox[0] / 1,
      y: viewBox[1] / 1,
      w: width,
      h: height,
      vW: viewBox[2],
      vH: viewBox[3]
    }
  }
  
  function getPath(path, percent) {
    const pathEl = is.str(path) ? selectString(path)[0] : path;
    const p = percent || 100;
    return function(property) {
      return {
        property,
        el: pathEl,
        svg: getParentSvg(pathEl),
        totalLength: getTotalLength(pathEl) * (p / 100)
      }
    }
  }
  
  function getPathProgress(path, progress, isPathTargetInsideSVG) {
    function point(offset = 0) {
      const l = progress + offset >= 1 ? progress + offset : 0;
      return path.el.getPointAtLength(l);
    }
    const svg = getParentSvg(path.el, path.svg)
    const p = point();
    const p0 = point(-1);
    const p1 = point(+1);
    const scaleX = isPathTargetInsideSVG ? 1 : svg.w / svg.vW;
    const scaleY = isPathTargetInsideSVG ? 1 : svg.h / svg.vH;
    switch (path.property) {
      case 'x': return (p.x - svg.x) * scaleX;
      case 'y': return (p.y - svg.y) * scaleY;
      case 'angle': return Math.atan2(p1.y - p0.y, p1.x - p0.x) * 180 / Math.PI;
    }
  }
  
  // Decompose value
  
  function decomposeValue(val, unit) {
    // const rgx = /-?\d*\.?\d+/g; // handles basic numbers
    // const rgx = /[+-]?\d+(?:\.\d+)?(?:[eE][+-]?\d+)?/g; // handles exponents notation
    const rgx = /[+-]?\d*\.?\d+(?:\.\d+)?(?:[eE][+-]?\d+)?/g; // handles exponents notation
    const value = validateValue((is.pth(val) ? val.totalLength : val), unit) + '';
    return {
      original: value,
      numbers: value.match(rgx) ? value.match(rgx).map(Number) : [0],
      strings: (is.str(val) || unit) ? value.split(rgx) : []
    }
  }
  
  // Animatables
  
  function parseTargets(targets) {
    const targetsArray = targets ? (flattenArray(is.arr(targets) ? targets.map(toArray) : toArray(targets))) : [];
    return filterArray(targetsArray, (item, pos, self) => self.indexOf(item) === pos);
  }
  
  function getAnimatables(targets) {
    const parsed = parseTargets(targets);
    return parsed.map((t, i) => {
      return {target: t, id: i, total: parsed.length, transforms: { list: getElementTransforms(t) } };
    });
  }
  
  // Properties
  
  function normalizePropertyTweens(prop, tweenSettings) {
    let settings = cloneObject(tweenSettings);
    // Override duration if easing is a spring
    if (/^spring/.test(settings.easing)) settings.duration = spring(settings.easing);
    if (is.arr(prop)) {
      const l = prop.length;
      const isFromTo = (l === 2 && !is.obj(prop[0]));
      if (!isFromTo) {
        // Duration divided by the number of tweens
        if (!is.fnc(tweenSettings.duration)) settings.duration = tweenSettings.duration / l;
      } else {
        // Transform [from, to] values shorthand to a valid tween value
        prop = {value: prop};
      }
    }
    const propArray = is.arr(prop) ? prop : [prop];
    return propArray.map((v, i) => {
      const obj = (is.obj(v) && !is.pth(v)) ? v : {value: v};
      // Default delay value should only be applied to the first tween
      if (is.und(obj.delay)) obj.delay = !i ? tweenSettings.delay : 0;
      // Default endDelay value should only be applied to the last tween
      if (is.und(obj.endDelay)) obj.endDelay = i === propArray.length - 1 ? tweenSettings.endDelay : 0;
      return obj;
    }).map(k => mergeObjects(k, settings));
  }
  
  
  function flattenKeyframes(keyframes) {
    const propertyNames = filterArray(flattenArray(keyframes.map(key => Object.keys(key))), p => is.key(p))
    .reduce((a,b) => { if (a.indexOf(b) < 0) a.push(b); return a; }, []);
    const properties = {};
    for (let i = 0; i < propertyNames.length; i++) {
      const propName = propertyNames[i];
      properties[propName] = keyframes.map(key => {
        const newKey = {};
        for (let p in key) {
          if (is.key(p)) {
            if (p == propName) newKey.value = key[p];
          } else {
            newKey[p] = key[p];
          }
        }
        return newKey;
      });
    }
    return properties;
  }
  
  function getProperties(tweenSettings, params) {
    const properties = [];
    const keyframes = params.keyframes;
    if (keyframes) params = mergeObjects(flattenKeyframes(keyframes), params);;
    for (let p in params) {
      if (is.key(p)) {
        properties.push({
          name: p,
          tweens: normalizePropertyTweens(params[p], tweenSettings)
        });
      }
    }
    return properties;
  }
  
  // Tweens
  
  function normalizeTweenValues(tween, animatable) {
    const t = {};
    for (let p in tween) {
      let value = getFunctionValue(tween[p], animatable);
      if (is.arr(value)) {
        value = value.map(v => getFunctionValue(v, animatable));
        if (value.length === 1) value = value[0];
      }
      t[p] = value;
    }
    t.duration = parseFloat(t.duration);
    t.delay = parseFloat(t.delay);
    return t;
  }
  
  function normalizeTweens(prop, animatable) {
    let previousTween;
    return prop.tweens.map(t => {
      const tween = normalizeTweenValues(t, animatable);
      const tweenValue = tween.value;
      let to = is.arr(tweenValue) ? tweenValue[1] : tweenValue;
      const toUnit = getUnit(to);
      const originalValue = getOriginalTargetValue(animatable.target, prop.name, toUnit, animatable);
      const previousValue = previousTween ? previousTween.to.original : originalValue;
      const from = is.arr(tweenValue) ? tweenValue[0] : previousValue;
      const fromUnit = getUnit(from) || getUnit(originalValue);
      const unit = toUnit || fromUnit;
      if (is.und(to)) to = previousValue;
      tween.from = decomposeValue(from, unit);
      tween.to = decomposeValue(getRelativeValue(to, from), unit);
      tween.start = previousTween ? previousTween.end : 0;
      tween.end = tween.start + tween.delay + tween.duration + tween.endDelay;
      tween.easing = parseEasings(tween.easing, tween.duration);
      tween.isPath = is.pth(tweenValue);
      tween.isPathTargetInsideSVG = tween.isPath && is.svg(animatable.target);
      tween.isColor = is.col(tween.from.original);
      if (tween.isColor) tween.round = 1;
      previousTween = tween;
      return tween;
    });
  }
  
  // Tween progress
  
  const setProgressValue = {
    css: (t, p, v) => t.style[p] = v,
    attribute: (t, p, v) => t.setAttribute(p, v),
    object: (t, p, v) => t[p] = v,
    transform: (t, p, v, transforms, manual) => {
      transforms.list.set(p, v);
      if (p === transforms.last || manual) {
        let str = '';
        transforms.list.forEach((value, prop) => { str += `${prop}(${value}) `; });
        t.style.transform = str;
      }
    }
  }
  
  // Set Value helper
  
  function setTargetsValue(targets, properties) {
    const animatables = getAnimatables(targets);
    animatables.forEach(animatable => {
      for (let property in properties) {
        const value = getFunctionValue(properties[property], animatable);
        const target = animatable.target;
        const valueUnit = getUnit(value);
        const originalValue = getOriginalTargetValue(target, property, valueUnit, animatable);
        const unit = valueUnit || getUnit(originalValue);
        const to = getRelativeValue(validateValue(value, unit), originalValue);
        const animType = getAnimationType(target, property);
        setProgressValue[animType](target, property, to, animatable.transforms, true);
      }
    });
  }
  
  // Animations
  
  function createAnimation(animatable, prop) {
    const animType = getAnimationType(animatable.target, prop.name);
    if (animType) {
      const tweens = normalizeTweens(prop, animatable);
      const lastTween = tweens[tweens.length - 1];
      return {
        type: animType,
        property: prop.name,
        animatable: animatable,
        tweens: tweens,
        duration: lastTween.end,
        delay: tweens[0].delay,
        endDelay: lastTween.endDelay
      }
    }
  }
  
  function getAnimations(animatables, properties) {
    return filterArray(flattenArray(animatables.map(animatable => {
      return properties.map(prop => {
        return createAnimation(animatable, prop);
      });
    })), a => !is.und(a));
  }
  
  // Create Instance
  
  function getInstanceTimings(animations, tweenSettings) {
    const animLength = animations.length;
    const getTlOffset = anim => anim.timelineOffset ? anim.timelineOffset : 0;
    const timings = {};
    timings.duration = animLength ? Math.max.apply(Math, animations.map(anim => getTlOffset(anim) + anim.duration)) : tweenSettings.duration;
    timings.delay = animLength ? Math.min.apply(Math, animations.map(anim => getTlOffset(anim) + anim.delay)) : tweenSettings.delay;
    timings.endDelay = animLength ? timings.duration - Math.max.apply(Math, animations.map(anim => getTlOffset(anim) + anim.duration - anim.endDelay)) : tweenSettings.endDelay;
    return timings;
  }
  
  let instanceID = 0;
  
  function createNewInstance(params) {
    const instanceSettings = replaceObjectProps(defaultInstanceSettings, params);
    const tweenSettings = replaceObjectProps(defaultTweenSettings, params);
    const properties = getProperties(tweenSettings, params);
    const animatables = getAnimatables(params.targets);
    const animations = getAnimations(animatables, properties);
    const timings = getInstanceTimings(animations, tweenSettings);
    const id = instanceID;
    instanceID++;
    return mergeObjects(instanceSettings, {
      id: id,
      children: [],
      animatables: animatables,
      animations: animations,
      duration: timings.duration,
      delay: timings.delay,
      endDelay: timings.endDelay
    });
  }
  
  // Core
  
  let activeInstances = [];
  
  const engine = (() => {
    let raf;
  
    function play() {
      if (!raf && (!isDocumentHidden() || !anime.suspendWhenDocumentHidden) && activeInstances.length > 0) {
        raf = requestAnimationFrame(step);
      }
    }
    function step(t) {
      // memo on algorithm issue:
      // dangerous iteration over mutable `activeInstances`
      // (that collection may be updated from within callbacks of `tick`-ed animation instances)
      let activeInstancesLength = activeInstances.length;
      let i = 0;
      while (i < activeInstancesLength) {
        const activeInstance = activeInstances[i];
        if (!activeInstance.paused) {
          activeInstance.tick(t);
          i++;
        } else {
          activeInstances.splice(i, 1);
          activeInstancesLength--;
        }
      }
      raf = i > 0 ? requestAnimationFrame(step) : undefined;
    }
  
    function handleVisibilityChange() {
      if (!anime.suspendWhenDocumentHidden) return;
  
      if (isDocumentHidden()) {
        // suspend ticks
        raf = cancelAnimationFrame(raf);
      } else { // is back to active tab
        // first adjust animations to consider the time that ticks were suspended
        activeInstances.forEach(
          instance => instance ._onDocumentVisibility()
        );
        engine();
      }
    }
    if (typeof document !== 'undefined') {
      document.addEventListener('visibilitychange', handleVisibilityChange);
    }
  
    return play;
  })();
  
  function isDocumentHidden() {
    return !!document && document.hidden;
  }
  
  // Public Instance
  
  function anime(params = {}) {
  
    let startTime = 0, lastTime = 0, now = 0;
    let children, childrenLength = 0;
    let resolve = null;
  
    function makePromise(instance) {
      const promise = window.Promise && new Promise(_resolve => resolve = _resolve);
      instance.finished = promise;
      return promise;
    }
  
    let instance = createNewInstance(params);
    let promise = makePromise(instance);
  
    function toggleInstanceDirection() {
      const direction = instance.direction;
      if (direction !== 'alternate') {
        instance.direction = direction !== 'normal' ? 'normal' : 'reverse';
      }
      instance.reversed = !instance.reversed;
      children.forEach(child => child.reversed = instance.reversed);
    }
  
    function adjustTime(time) {
      return instance.reversed ? instance.duration - time : time;
    }
  
    function resetTime() {
      startTime = 0;
      lastTime = adjustTime(instance.currentTime) * (1 / anime.speed);
    }
  
    function seekChild(time, child) {
      if (child) child.seek(time - child.timelineOffset);
    }
  
    function syncInstanceChildren(time) {
      if (!instance.reversePlayback) {
        for (let i = 0; i < childrenLength; i++) seekChild(time, children[i]);
      } else {
        for (let i = childrenLength; i--;) seekChild(time, children[i]);
      }
    }
  
    function setAnimationsProgress(insTime) {
      let i = 0;
      const animations = instance.animations;
      const animationsLength = animations.length;
      while (i < animationsLength) {
        const anim = animations[i];
        const animatable = anim.animatable;
        const tweens = anim.tweens;
        const tweenLength = tweens.length - 1;
        let tween = tweens[tweenLength];
        // Only check for keyframes if there is more than one tween
        if (tweenLength) tween = filterArray(tweens, t => (insTime < t.end))[0] || tween;
        const elapsed = minMax(insTime - tween.start - tween.delay, 0, tween.duration) / tween.duration;
        const eased = isNaN(elapsed) ? 1 : tween.easing(elapsed);
        const strings = tween.to.strings;
        const round = tween.round;
        const numbers = [];
        const toNumbersLength = tween.to.numbers.length;
        let progress;
        for (let n = 0; n < toNumbersLength; n++) {
          let value;
          const toNumber = tween.to.numbers[n];
          const fromNumber = tween.from.numbers[n] || 0;
          if (!tween.isPath) {
            value = fromNumber + (eased * (toNumber - fromNumber));
          } else {
            value = getPathProgress(tween.value, eased * toNumber, tween.isPathTargetInsideSVG);
          }
          if (round) {
            if (!(tween.isColor && n > 2)) {
              value = Math.round(value * round) / round;
            }
          }
          numbers.push(value);
        }
        // Manual Array.reduce for better performances
        const stringsLength = strings.length;
        if (!stringsLength) {
          progress = numbers[0];
        } else {
          progress = strings[0];
          for (let s = 0; s < stringsLength; s++) {
            const a = strings[s];
            const b = strings[s + 1];
            const n = numbers[s];
            if (!isNaN(n)) {
              if (!b) {
                progress += n + ' ';
              } else {
                progress += n + b;
              }
            }
          }
        }
        setProgressValue[anim.type](animatable.target, anim.property, progress, animatable.transforms);
        anim.currentValue = progress;
        i++;
      }
    }
  
    function setCallback(cb) {
      if (instance[cb] && !instance.passThrough) instance[cb](instance);
    }
  
    function countIteration() {
      if (instance.remaining && instance.remaining !== true) {
        instance.remaining--;
      }
    }
  
    function setInstanceProgress(engineTime) {
      const insDuration = instance.duration;
      const insDelay = instance.delay;
      const insEndDelay = insDuration - instance.endDelay;
      const insTime = adjustTime(engineTime);
      instance.progress = minMax((insTime / insDuration) * 100, 0, 100);
      instance.reversePlayback = insTime < instance.currentTime;
      if (children) { syncInstanceChildren(insTime); }
      if (!instance.began && instance.currentTime > 0) {
        instance.began = true;
        setCallback('begin');
      }
      if (!instance.loopBegan && instance.currentTime > 0) {
        instance.loopBegan = true;
        setCallback('loopBegin');
      }
      if (insTime <= insDelay && instance.currentTime !== 0) {
        setAnimationsProgress(0);
      }
      if ((insTime >= insEndDelay && instance.currentTime !== insDuration) || !insDuration) {
        setAnimationsProgress(insDuration);
      }
      if (insTime > insDelay && insTime < insEndDelay) {
        if (!instance.changeBegan) {
          instance.changeBegan = true;
          instance.changeCompleted = false;
          setCallback('changeBegin');
        }
        setCallback('change');
        setAnimationsProgress(insTime);
      } else {
        if (instance.changeBegan) {
          instance.changeCompleted = true;
          instance.changeBegan = false;
          setCallback('changeComplete');
        }
      }
      instance.currentTime = minMax(insTime, 0, insDuration);
      if (instance.began) setCallback('update');
      if (engineTime >= insDuration) {
        lastTime = 0;
        countIteration();
        if (!instance.remaining) {
          instance.paused = true;
          if (!instance.completed) {
            instance.completed = true;
            setCallback('loopComplete');
            setCallback('complete');
            if (!instance.passThrough && 'Promise' in window) {
              resolve();
              promise = makePromise(instance);
            }
          }
        } else {
          startTime = now;
          setCallback('loopComplete');
          instance.loopBegan = false;
          if (instance.direction === 'alternate') {
            toggleInstanceDirection();
          }
        }
      }
    }
  
    instance.reset = function() {
      const direction = instance.direction;
      instance.passThrough = false;
      instance.currentTime = 0;
      instance.progress = 0;
      instance.paused = true;
      instance.began = false;
      instance.loopBegan = false;
      instance.changeBegan = false;
      instance.completed = false;
      instance.changeCompleted = false;
      instance.reversePlayback = false;
      instance.reversed = direction === 'reverse';
      instance.remaining = instance.loop;
      children = instance.children;
      childrenLength = children.length;
      for (let i = childrenLength; i--;) instance.children[i].reset();
      if (instance.reversed && instance.loop !== true || (direction === 'alternate' && instance.loop === 1)) instance.remaining++;
      setAnimationsProgress(instance.reversed ? instance.duration : 0);
    }
  
    // internal method (for engine) to adjust animation timings before restoring engine ticks (rAF)
    instance._onDocumentVisibility = resetTime;
  
    // Set Value helper
  
    instance.set = function(targets, properties) {
      setTargetsValue(targets, properties);
      return instance;
    }
  
    instance.tick = function(t) {
      now = t;
      if (!startTime) startTime = now;
      setInstanceProgress((now + (lastTime - startTime)) * anime.speed);
    }
  
    instance.seek = function(time) {
      setInstanceProgress(adjustTime(time));
    }
  
    instance.pause = function() {
      instance.paused = true;
      resetTime();
    }
  
    instance.play = function() {
      if (!instance.paused) return;
      if (instance.completed) instance.reset();
      instance.paused = false;
      activeInstances.push(instance);
      resetTime();
      engine();
    }
  
    instance.reverse = function() {
      toggleInstanceDirection();
      instance.completed = instance.reversed ? false : true;
      resetTime();
    }
  
    instance.restart = function() {
      instance.reset();
      instance.play();
    }
  
    instance.remove = function(targets) {
      const targetsArray = parseTargets(targets);
      removeTargetsFromInstance(targetsArray, instance);
    }
  
    instance.reset();
  
    if (instance.autoplay) instance.play();
  
    return instance;
  
  }
  
  // Remove targets from animation
  
  function removeTargetsFromAnimations(targetsArray, animations) {
    for (let a = animations.length; a--;) {
      if (arrayContains(targetsArray, animations[a].animatable.target)) {
        animations.splice(a, 1);
      }
    }
  }
  
  function removeTargetsFromInstance(targetsArray, instance) {
    const animations = instance.animations;
    const children = instance.children;
    removeTargetsFromAnimations(targetsArray, animations);
    for (let c = children.length; c--;) {
      const child = children[c];
      const childAnimations = child.animations;
      removeTargetsFromAnimations(targetsArray, childAnimations);
      if (!childAnimations.length && !child.children.length) children.splice(c, 1);
    }
    if (!animations.length && !children.length) instance.pause();
  }
  
  function removeTargetsFromActiveInstances(targets) {
    const targetsArray = parseTargets(targets);
    for (let i = activeInstances.length; i--;) {
      const instance = activeInstances[i];
      removeTargetsFromInstance(targetsArray, instance);
    }
  }
  
  // Stagger helpers
  
  function stagger(val, params = {}) {
    const direction = params.direction || 'normal';
    const easing = params.easing ? parseEasings(params.easing) : null;
    const grid = params.grid;
    const axis = params.axis;
    let fromIndex = params.from || 0;
    const fromFirst = fromIndex === 'first';
    const fromCenter = fromIndex === 'center';
    const fromLast = fromIndex === 'last';
    const isRange = is.arr(val);
    const val1 = isRange ? parseFloat(val[0]) : parseFloat(val);
    const val2 = isRange ? parseFloat(val[1]) : 0;
    const unit = getUnit(isRange ? val[1] : val) || 0;
    const start = params.start || 0 + (isRange ? val1 : 0);
    let values = [];
    let maxValue = 0;
    return (el, i, t) => {
      if (fromFirst) fromIndex = 0;
      if (fromCenter) fromIndex = (t - 1) / 2;
      if (fromLast) fromIndex = t - 1;
      if (!values.length) {
        for (let index = 0; index < t; index++) {
          if (!grid) {
            values.push(Math.abs(fromIndex - index));
          } else {
            const fromX = !fromCenter ? fromIndex%grid[0] : (grid[0]-1)/2;
            const fromY = !fromCenter ? Math.floor(fromIndex/grid[0]) : (grid[1]-1)/2;
            const toX = index%grid[0];
            const toY = Math.floor(index/grid[0]);
            const distanceX = fromX - toX;
            const distanceY = fromY - toY;
            let value = Math.sqrt(distanceX * distanceX + distanceY * distanceY);
            if (axis === 'x') value = -distanceX;
            if (axis === 'y') value = -distanceY;
            values.push(value);
          }
          maxValue = Math.max(...values);
        }
        if (easing) values = values.map(val => easing(val / maxValue) * maxValue);
        if (direction === 'reverse') values = values.map(val => axis ? (val < 0) ? val * -1 : -val : Math.abs(maxValue - val));
      }
      const spacing = isRange ? (val2 - val1) / maxValue : val1;
      return start + (spacing * (Math.round(values[i] * 100) / 100)) + unit;
    }
  }
  
  // Timeline
  
  function timeline(params = {}) {
    let tl = anime(params);
    tl.duration = 0;
    tl.add = function(instanceParams, timelineOffset) {
      const tlIndex = activeInstances.indexOf(tl);
      const children = tl.children;
      if (tlIndex > -1) activeInstances.splice(tlIndex, 1);
      function passThrough(ins) { ins.passThrough = true; };
      for (let i = 0; i < children.length; i++) passThrough(children[i]);
      let insParams = mergeObjects(instanceParams, replaceObjectProps(defaultTweenSettings, params));
      insParams.targets = insParams.targets || params.targets;
      const tlDuration = tl.duration;
      insParams.autoplay = false;
      insParams.direction = tl.direction;
      insParams.timelineOffset = is.und(timelineOffset) ? tlDuration : getRelativeValue(timelineOffset, tlDuration);
      passThrough(tl);
      tl.seek(insParams.timelineOffset);
      const ins = anime(insParams);
      passThrough(ins);
      const totalDuration = ins.duration + insParams.timelineOffset;
      children.push(ins);
      const timings = getInstanceTimings(children, params);
      tl.delay = timings.delay;
      tl.endDelay = timings.endDelay;
      tl.duration = timings.duration;
      tl.seek(0);
      tl.reset();
      if (tl.autoplay) tl.play();
      return tl;
    }
    return tl;
  }
  
  anime.version = '3.2.1';
  anime.speed = 1;
  // TODO:#review: naming, documentation
  anime.suspendWhenDocumentHidden = true;
  anime.running = activeInstances;
  anime.remove = removeTargetsFromActiveInstances;
  anime.get = getOriginalTargetValue;
  anime.set = setTargetsValue;
  anime.convertPx = convertPxToUnit;
  anime.path = getPath;
  anime.setDashoffset = setDashoffset;
  anime.stagger = stagger;
  anime.timeline = timeline;
  anime.easing = parseEasings;
  anime.penner = penner;
  anime.random = (min, max) => Math.floor(Math.random() * (max - min + 1)) + min;
  
  export default anime;
  