Snow.js

```
/\*\* @license
 \* DHTML Snowstorm! JavaScript-based snow for web pages
 \* Making it snow on the internets since 2003. You're welcome.
 \* -----------------------------------------------------------
 \* Version 1.44.20131208 (Previous rev: 1.44.20131125)
 \* Copyright (c) 2007, Scott Schiller. All rights reserved.
 \* Code provided under the BSD License
 \* http://schillmania.com/projects/snowstorm/license.txt
 \*/

/\*jslint nomen: true, plusplus: true, sloppy: true, vars: true, white: true \*/
/\*global window, document, navigator, clearInterval, setInterval \*/

var snowStorm = (function(window, document) {

 // --- common properties ---

 this.autoStart = true; // Whether the snow should start automatically or not.
 this.excludeMobile = true; // Snow is likely to be bad news for mobile phones' CPUs (and batteries.) Enable at your own risk.
 this.flakesMax = 128; // Limit total amount of snow made (falling + sticking)
 this.flakesMaxActive = 64; // Limit amount of snow falling at once (less = lower CPU use)
 this.animationInterval = 50; // Theoretical "miliseconds per frame" measurement. 20 = fast + smooth, but high CPU use. 50 = more conservative, but slower
 this.useGPU = true; // Enable transform-based hardware acceleration, reduce CPU load.
 this.className = null; // CSS class name for further customization on snow elements
 this.excludeMobile = true; // Snow is likely to be bad news for mobile phones' CPUs (and batteries.) By default, be nice.
 this.flakeBottom = null; // Integer for Y axis snow limit, 0 or null for "full-screen" snow effect
 this.followMouse = false; // Snow movement can respond to the user's mouse
 this.snowColor = '#fff'; // Don't eat (or use?) yellow snow.
 this.snowCharacter = '&bull;'; // &bull; = bullet, &middot; is square on some systems etc.
 this.snowStick = true; // Whether or not snow should "stick" at the bottom. When off, will never collect.
 this.targetElement = null; // element which snow will be appended to (null = document.body) - can be an element ID eg. 'myDiv', or a DOM node reference
 this.useMeltEffect = true; // When recycling fallen snow (or rarely, when falling), have it "melt" and fade out if browser supports it
 this.useTwinkleEffect = false; // Allow snow to randomly "flicker" in and out of view while falling
 this.usePositionFixed = false; // true = snow does not shift vertically when scrolling. May increase CPU load, disabled by default - if enabled, used only where supported
 this.usePixelPosition = false; // Whether to use pixel values for snow top/left vs. percentages. Auto-enabled if body is position:relative or targetElement is specified.

 // --- less-used bits ---

 this.freezeOnBlur = true; // Only snow when the window is in focus (foreground.) Saves CPU.
 this.flakeLeftOffset = 0; // Left margin/gutter space on edge of container (eg. browser window.) Bump up these values if seeing horizontal scrollbars.
 this.flakeRightOffset = 0; // Right margin/gutter space on edge of container
 this.flakeWidth = 8; // Max pixel width reserved for snow element
 this.flakeHeight = 8; // Max pixel height reserved for snow element
 this.vMaxX = 5; // Maximum X velocity range for snow
 this.vMaxY = 4; // Maximum Y velocity range for snow
 this.zIndex = 0; // CSS stacking order applied to each snowflake

 // --- "No user-serviceable parts inside" past this point, yadda yadda ---

 var storm = this,
 features,
 // UA sniffing and backCompat rendering mode checks for fixed position, etc.
 isIE = navigator.userAgent.match(/msie/i),
 isIE6 = navigator.userAgent.match(/msie 6/i),
 isMobile = navigator.userAgent.match(/mobile|opera m(ob|in)/i),
 isBackCompatIE = (isIE && document.compatMode === 'BackCompat'),
 noFixed = (isBackCompatIE || isIE6),
 screenX = null, screenX2 = null, screenY = null, scrollY = null, docHeight = null, vRndX = null, vRndY = null,
 windOffset = 1,
 windMultiplier = 2,
 flakeTypes = 6,
 fixedForEverything = false,
 targetElementIsRelative = false,
 opacitySupported = (function(){
 try {
 document.createElement('div').style.opacity = '0.5';
 } catch(e) {
 return false;
 }
 return true;
 }()),
 didInit = false,
 docFrag = document.createDocumentFragment();

 features = (function() {

 var getAnimationFrame;

 /\*\*
 \* hat tip: paul irish
 \* http://paulirish.com/2011/requestanimationframe-for-smart-animating/
 \* https://gist.github.com/838785
 \*/

 function timeoutShim(callback) {
 window.setTimeout(callback, 1000/(storm.animationInterval || 20));
 }

 timeoutShim);

 // apply to window, avoid "illegal invocation" errors in Chrome
 getAnimationFrame = \_animationFrame ? function() {
 return \_animationFrame.apply(window, arguments);
 } : null;

 var testDiv;

 testDiv = document.createElement('div');

 function has(prop) {

 // test for feature support
 var result = testDiv.style[prop];
 return (result !== undefined ? prop : null);

 }

 // note local scope.
 var localFeatures = {

 transform: {
 ie: has('-ms-transform'),
 moz: has('MozTransform'),
 opera: has('OTransform'),
 webkit: has('webkitTransform'),
 w3: has('transform'),
 prop: null // the normalized property value
 },

 getAnimationFrame: getAnimationFrame

 };

 localFeatures.transform.prop = (
 localFeatures.transform.opera
 );

 testDiv = null;

 return localFeatures;

 }());

 this.timer = null;
 this.flakes = [];
 this.disabled = false;
 this.active = false;
 this.meltFrameCount = 20;
 this.meltFrames = [];

 this.setXY = function(o, x, y) {

 if (!o) {
 return false;
 }

 if (storm.usePixelPosition || targetElementIsRelative) {

 o.style.left = (x - storm.flakeWidth) + 'px';
 o.style.top = (y - storm.flakeHeight) + 'px';

 } else if (noFixed) {

 o.style.right = (100-(x/screenX\*100)) + '%';
 // avoid creating vertical scrollbars
 o.style.top = (Math.min(y, docHeight-storm.flakeHeight)) + 'px';

 } else {

 if (!storm.flakeBottom) {

 // if not using a fixed bottom coordinate...
 o.style.right = (100-(x/screenX\*100)) + '%';
 o.style.bottom = (100-(y/screenY\*100)) + '%';

 } else {

 // absolute top.
 o.style.right = (100-(x/screenX\*100)) + '%';
 o.style.top = (Math.min(y, docHeight-storm.flakeHeight)) + 'px';

 }

 }

 };

 this.events = (function() {

 var old = (!window.addEventListener && window.attachEvent), slice = Array.prototype.slice,
 evt = {
 add: (old?'attachEvent':'addEventListener'),
 remove: (old?'detachEvent':'removeEventListener')
 };

 function getArgs(oArgs) {
 var args = slice.call(oArgs), len = args.length;
 if (old) {
 args[1] = 'on' + args[1]; // prefix
 if (len > 3) {
 args.pop(); // no capture
 }
 } else if (len === 3) {
 args.push(false);
 }
 return args;
 }

 function apply(args, sType) {
 var element = args.shift(),
 method = [evt[sType]];
 if (old) {
 element[method](args[0], args[1]);
 } else {
 element[method].apply(element, args);
 }
 }

 function addEvent() {
 apply(getArgs(arguments), 'add');
 }

 function removeEvent() {
 apply(getArgs(arguments), 'remove');
 }

 return {
 add: addEvent,
 remove: removeEvent
 };

 }());

 function rnd(n,min) {
 if (isNaN(min)) {
 min = 0;
 }
 return (Math.random()\*n)+min;
 }

 function plusMinus(n) {
 return (parseInt(rnd(2),10)===1?n\*-1:n);
 }

 this.randomizeWind = function() {
 var i;
 vRndX = plusMinus(rnd(storm.vMaxX,0.2));
 vRndY = rnd(storm.vMaxY,0.2);
 if (this.flakes) {
 for (i=0; i<this.flakes.length; i++) {
 if (this.flakes[i].active) {
 this.flakes[i].setVelocities();
 }
 }
 }
 };

 this.scrollHandler = function() {
 var i;
 // "attach" snowflakes to bottom of window if no absolute bottom value was given
 if (isNaN(scrollY)) {
 scrollY = 0; // Netscape 6 scroll fix
 }
 if (!fixedForEverything && !storm.flakeBottom && storm.flakes) {
 for (i=0; i<storm.flakes.length; i++) {
 if (storm.flakes[i].active === 0) {
 storm.flakes[i].stick();
 }
 }
 }
 };

 this.resizeHandler = function() {
 if (window.innerWidth || window.innerHeight) {
 screenX = window.innerWidth - 16 - storm.flakeRightOffset;
 screenY = (storm.flakeBottom || window.innerHeight);
 } else {
 }
 docHeight = document.body.offsetHeight;
 screenX2 = parseInt(screenX/2,10);
 };

 this.resizeHandlerAlt = function() {
 screenX = storm.targetElement.offsetWidth - storm.flakeRightOffset;
 screenY = storm.flakeBottom || storm.targetElement.offsetHeight;
 screenX2 = parseInt(screenX/2,10);
 docHeight = document.body.offsetHeight;
 };

 this.freeze = function() {
 // pause animation
 if (!storm.disabled) {
 storm.disabled = 1;
 } else {
 return false;
 }
 storm.timer = null;
 };

 this.resume = function() {
 if (storm.disabled) {
 storm.disabled = 0;
 } else {
 return false;
 }
 storm.timerInit();
 };

 this.toggleSnow = function() {
 if (!storm.flakes.length) {
 // first run
 storm.start();
 } else {
 storm.active = !storm.active;
 if (storm.active) {
 storm.show();
 storm.resume();
 } else {
 storm.stop();
 storm.freeze();
 }
 }
 };

 this.stop = function() {
 var i;
 this.freeze();
 for (i=0; i<this.flakes.length; i++) {
 this.flakes[i].o.style.display = 'none';
 }
 storm.events.remove(window,'scroll',storm.scrollHandler);
 storm.events.remove(window,'resize',storm.resizeHandler);
 if (storm.freezeOnBlur) {
 if (isIE) {
 storm.events.remove(document,'focusout',storm.freeze);
 storm.events.remove(document,'focusin',storm.resume);
 } else {
 storm.events.remove(window,'blur',storm.freeze);
 storm.events.remove(window,'focus',storm.resume);
 }
 }
 };

 this.show = function() {
 var i;
 for (i=0; i<this.flakes.length; i++) {
 this.flakes[i].o.style.display = 'block';
 }
 };

 this.SnowFlake = function(type,x,y) {
 var s = this;
 this.type = type;
 this.x = x||parseInt(rnd(screenX-20),10);
 this.y = (!isNaN(y)?y:-rnd(screenY)-12);
 this.vX = null;
 this.vY = null;
 this.vAmpTypes = [1,1.2,1.4,1.6,1.8]; // "amplification" for vX/vY (based on flake size/type)
 this.vAmp = this.vAmpTypes[this.type] || 1;
 this.melting = false;
 this.meltFrameCount = storm.meltFrameCount;
 this.meltFrames = storm.meltFrames;
 this.meltFrame = 0;
 this.twinkleFrame = 0;
 this.active = 1;
 this.fontSize = (10+(this.type/5)\*10);
 this.o = document.createElement('div');
 this.o.innerHTML = storm.snowCharacter;
 if (storm.className) {
 this.o.setAttribute('class', storm.className);
 }
 this.o.style.color = storm.snowColor;
 this.o.style.position = (fixedForEverything?'fixed':'absolute');
 if (storm.useGPU && features.transform.prop) {
 // GPU-accelerated snow.
 this.o.style[features.transform.prop] = 'translate3d(0px, 0px, 0px)';
 }
 this.o.style.width = storm.flakeWidth+'px';
 this.o.style.height = storm.flakeHeight+'px';
 this.o.style.fontFamily = 'arial,verdana';
 this.o.style.cursor = 'default';
 this.o.style.overflow = 'hidden';
 this.o.style.fontWeight = 'normal';
 this.o.style.zIndex = storm.zIndex;
 docFrag.appendChild(this.o);

 this.refresh = function() {
 if (isNaN(s.x) || isNaN(s.y)) {
 // safety check
 return false;
 }
 storm.setXY(s.o, s.x, s.y);
 };

 this.stick = function() {
 if (noFixed || (storm.targetElement !== document.documentElement && storm.targetElement !== document.body)) {
 s.o.style.top = (screenY+scrollY-storm.flakeHeight)+'px';
 } else if (storm.flakeBottom) {
 s.o.style.top = storm.flakeBottom+'px';
 } else {
 s.o.style.display = 'none';
 s.o.style.bottom = '0%';
 s.o.style.position = 'fixed';
 s.o.style.display = 'block';
 }
 };

 this.vCheck = function() {
 if (s.vX>=0 && s.vX<0.2) {
 s.vX = 0.2;
 } else if (s.vX<0 && s.vX>-0.2) {
 s.vX = -0.2;
 }
 if (s.vY>=0 && s.vY<0.2) {
 s.vY = 0.2;
 }
 };

 this.move = function() {
 var vX = s.vX\*windOffset, yDiff;
 s.x += vX;
 s.y += (s.vY\*s.vAmp);
 if (s.x >= screenX || screenX-s.x < storm.flakeWidth) { // X-axis scroll check
 s.x = 0;
 } else if (vX < 0 && s.x-storm.flakeLeftOffset < -storm.flakeWidth) {
 s.x = screenX-storm.flakeWidth-1; // flakeWidth;
 }
 s.refresh();
 yDiff = screenY+scrollY-s.y+storm.flakeHeight;
 if (yDiff<storm.flakeHeight) {
 s.active = 0;
 if (storm.snowStick) {
 s.stick();
 } else {
 s.recycle();
 }
 } else {
 if (storm.useMeltEffect && s.active && s.type < 3 && !s.melting && Math.random()>0.998) {
 // ~1/1000 chance of melting mid-air, with each frame
 s.melting = true;
 s.melt();
 // only incrementally melt one frame
 // s.melting = false;
 }
 if (storm.useTwinkleEffect) {
 if (s.twinkleFrame < 0) {
 if (Math.random() > 0.97) {
 s.twinkleFrame = parseInt(Math.random() \* 8, 10);
 }
 } else {
 s.twinkleFrame--;
 if (!opacitySupported) {
 s.o.style.visibility = (s.twinkleFrame && s.twinkleFrame % 2 === 0 ? 'hidden' : 'visible');
 } else {
 s.o.style.opacity = (s.twinkleFrame && s.twinkleFrame % 2 === 0 ? 0 : 1);
 }
 }
 }
 }
 };

 this.animate = function() {
 // main animation loop
 // move, check status, die etc.
 s.move();
 };

 this.setVelocities = function() {
 s.vX = vRndX+rnd(storm.vMaxX\*0.12,0.1);
 s.vY = vRndY+rnd(storm.vMaxY\*0.12,0.1);
 };

 this.setOpacity = function(o,opacity) {
 if (!opacitySupported) {
 return false;
 }
 o.style.opacity = opacity;
 };

 this.melt = function() {
 if (!storm.useMeltEffect || !s.melting) {
 s.recycle();
 } else {
 if (s.meltFrame < s.meltFrameCount) {
 s.setOpacity(s.o,s.meltFrames[s.meltFrame]);
 s.o.style.fontSize = s.fontSize-(s.fontSize\*(s.meltFrame/s.meltFrameCount))+'px';
 s.o.style.lineHeight = storm.flakeHeight+2+(storm.flakeHeight\*0.75\*(s.meltFrame/s.meltFrameCount))+'px';
 s.meltFrame++;
 } else {
 s.recycle();
 }
 }
 };

 this.recycle = function() {
 s.o.style.display = 'none';
 s.o.style.position = (fixedForEverything?'fixed':'absolute');
 s.o.style.bottom = 'auto';
 s.setVelocities();
 s.vCheck();
 s.meltFrame = 0;
 s.melting = false;
 s.setOpacity(s.o,1);
 s.o.style.padding = '0px';
 s.o.style.margin = '0px';
 s.o.style.fontSize = s.fontSize+'px';
 s.o.style.lineHeight = (storm.flakeHeight+2)+'px';
 s.o.style.textAlign = 'center';
 s.o.style.verticalAlign = 'baseline';
 s.x = parseInt(rnd(screenX-storm.flakeWidth-20),10);
 s.y = parseInt(rnd(screenY)\*-1,10)-storm.flakeHeight;
 s.refresh();
 s.o.style.display = 'block';
 s.active = 1;
 };

 this.recycle(); // set up x/y coords etc.
 this.refresh();

 };

 this.snow = function() {
 var active = 0, flake = null, i, j;
 for (i=0, j=storm.flakes.length; i<j; i++) {
 if (storm.flakes[i].active === 1) {
 storm.flakes[i].move();
 active++;
 }
 if (storm.flakes[i].melting) {
 storm.flakes[i].melt();
 }
 }
 if (active<storm.flakesMaxActive) {
 flake = storm.flakes[parseInt(rnd(storm.flakes.length),10)];
 if (flake.active === 0) {
 flake.melting = true;
 }
 }
 if (storm.timer) {
 features.getAnimationFrame(storm.snow);
 }
 };

 this.mouseMove = function(e) {
 if (!storm.followMouse) {
 return true;
 }
 var x = parseInt(e.clientX,10);
 if (x<screenX2) {
 windOffset = -windMultiplier+(x/screenX2\*windMultiplier);
 } else {
 x -= screenX2;
 windOffset = (x/screenX2)\*windMultiplier;
 }
 };

 this.createSnow = function(limit,allowInactive) {
 var i;
 for (i=0; i<limit; i++) {
 storm.flakes[storm.flakes.length] = new storm.SnowFlake(parseInt(rnd(flakeTypes),10));
 if (allowInactive || i>storm.flakesMaxActive) {
 storm.flakes[storm.flakes.length-1].active = -1;
 }
 }
 storm.targetElement.appendChild(docFrag);
 };

 this.timerInit = function() {
 storm.timer = true;
 storm.snow();
 };

 this.init = function() {
 var i;
 for (i=0; i<storm.meltFrameCount; i++) {
 storm.meltFrames.push(1-(i/storm.meltFrameCount));
 }
 storm.randomizeWind();
 storm.createSnow(storm.flakesMax); // create initial batch
 storm.events.add(window,'resize',storm.resizeHandler);
 storm.events.add(window,'scroll',storm.scrollHandler);
 if (storm.freezeOnBlur) {
 if (isIE) {
 storm.events.add(document,'focusout',storm.freeze);
 storm.events.add(document,'focusin',storm.resume);
 } else {
 storm.events.add(window,'blur',storm.freeze);
 storm.events.add(window,'focus',storm.resume);
 }
 }
 storm.resizeHandler();
 storm.scrollHandler();
 if (storm.followMouse) {
 storm.events.add(isIE?document:window,'mousemove',storm.mouseMove);
 }
 storm.animationInterval = Math.max(20,storm.animationInterval);
 storm.timerInit();
 };

 this.start = function(bFromOnLoad) {
 if (!didInit) {
 didInit = true;
 } else if (bFromOnLoad) {
 // already loaded and running
 return true;
 }
 if (typeof storm.targetElement === 'string') {
 var targetID = storm.targetElement;
 storm.targetElement = document.getElementById(targetID);
 if (!storm.targetElement) {
 throw new Error('Snowstorm: Unable to get targetElement "'+targetID+'"');
 }
 }
 if (!storm.targetElement) {
 storm.targetElement = (document.body || document.documentElement);
 }
 if (storm.targetElement !== document.documentElement && storm.targetElement !== document.body) {
 // re-map handler to get element instead of screen dimensions
 storm.resizeHandler = storm.resizeHandlerAlt;
 //and force-enable pixel positioning
 storm.usePixelPosition = true;
 }
 storm.resizeHandler(); // get bounding box elements
 storm.usePositionFixed = (storm.usePositionFixed && !noFixed && !storm.flakeBottom); // whether or not position:fixed is to be used
 if (window.getComputedStyle) {
 // attempt to determine if body or user-specified snow parent element is relatlively-positioned.
 try {
 targetElementIsRelative = (window.getComputedStyle(storm.targetElement, null).getPropertyValue('position') === 'relative');
 } catch(e) {
 // oh well
 targetElementIsRelative = false;
 }
 }
 fixedForEverything = storm.usePositionFixed;
 if (screenX && screenY && !storm.disabled) {
 storm.init();
 storm.active = true;
 }
 };

 function doDelayedStart() {
 window.setTimeout(function() {
 storm.start(true);
 }, 20);
 // event cleanup
 storm.events.remove(isIE?document:window,'mousemove',doDelayedStart);
 }

 function doStart() {
 if (!storm.excludeMobile || !isMobile) {
 doDelayedStart();
 }
 // event cleanup
 storm.events.remove(window, 'load', doStart);
 }

 // hooks for starting the snow
 if (storm.autoStart) {
 storm.events.add(window, 'load', doStart, false);
 }

 return this;

}(window, document));

```