Stand-alone parallax scrolling JavaScript library in about 12k minified.
Designer friendly. No JavaScript skills needed. Just plain CSS and HTML.
Actually, skrollr is much more than "just" parallax scrolling. It's a full-fledged scrolling animation library. In fact, you can use it and still have no parallax scrolling at all. But I wanted to sound hip and use some buzz-words. By the way, skrollr leverages HTML5 and CSS3 ;-)
- skrollr-menu - Hash navigation
- skrollr-ie - IE < 9 CSS fixes
- skrollr-stylesheets - Keyframes inside CSS files
- skrollr-colors - Mix and match hex, rgb and hsl colors.
- skrollr-decks - Fullpage presentation decks.
Moved to the wiki.
First of all: look at the examples and read the source ;-). This might give you a feeling of how stuff works and you can see how some patterns can be implemented.
skrollr allows you to animate any CSS property of any element depending on the horizontal scrollbar position. All you need to do is define key frames for each element at certain points in top scroll offset.
Other libraries require you to write JavaScript in order to define your animations. This introduces two main problems:
- Animation and element are not at one place. In order to find out if any animations are defined for a given element, you have to scroll through many (sometimes thousands) of lines of JavaScript.
- You have to learn a new syntax which is often very verbose and limited at the same time.
With skrollr, you put the definition of your key frames right where they belong (to the element) using a syntax you already know (plain CSS).
If you would rather have the keyframes inside a separate file, take a look at skrollr-stylesheets.
If you prefer to use JavaScript to define your animations make sure to take a look at ScrollMagic. It depends on both jQuery and the Greensock Animation Platform (GSAP) and gives you full control over every detail of your animations.
First of all you want to include the skrollr.min.js file at the bottom of your document (right before the closing </body>) and then call skrollr.init(). Or you can place it inside the <head> if you want to, but make sure to call init() once the document has been loaded (e.g. jQuery's ready event or even window.onload).
<script type="text/javascript" src="skrollr.min.js"></script>
<script type="text/javascript">
var s = skrollr.init();
</script>
</body>If you are using require.js to structure your project, you can use skrollr as a module as well.
require(['skrollr'], function(skrollr){
var s = skrollr.init();
});If you're familiar with CSS, you already know the style attribute. In order to create an animation you would need several, at least two, of them. That's what skrollr does. You use the HTML5 data- attributes to define multiple sets of styles (we call each of them keyframe) and skrollr interpolates between them.
Let's change the background-color of a div starting at #00f when the scrollbar is at the top and ending with #f00 when the user scrolled 500 pixels down
<div data-0="background-color:rgb(0,0,255);" data-500="background-color:rgb(255,0,0);">WOOOT</div>- Skrollr ensures that you can actually scroll down 500 pixels or more, even if there's not enough content. You can suppress this by using the
forceHeightoption. - You can't use
#00for#0000ff. You need to usergborhsland explicitly decide which color space you want because they result in different animations (HSL is much cooler most of the time). Don't worry, the IE plugin teaches IE < 9 to displayrgbandhslcorrectly.
<div data-0="background-color:rgb(0,0,255);transform:rotate(0deg);" data-500="background-color:rgb(255,0,0);transform:rotate(360deg);">WOOOT</div>- Skrollr handles all these nasty CSS prefixes for you. Just -moz-relax and get yourself a cup of -webkit-coffee.
<div data-0="background-color:rgb(0,0,255);transform[bounce]:rotate(0deg);" data-500="background-color:rgb(255,0,0);transform[bounce]:rotate(360deg);">WOOOT</div>- Skrollr allows non-linear animations. The so called easing functions can be used per-property by putting them in square brackets behind the property. There's a built-in list of easing functions (see below in the JavaScript section) and you can use your own functions by using the
easingsoptions.
Now you may have noticed that using 500 as a keyframe position is kind of random and the look depends on your browser size.
Let's have the animation end when the top of the element reaches the top of the viewport (element leaves the viewport)
<div data-0="background-color:rgb(0,0,255);transform[bounce]:rotate(0deg);" data-top="background-color:rgb(255,0,0);transform[bounce]:rotate(360deg);">WOOOT</div>That's the end of this short intro. The following sections will explain some more things in detail.
If you're not a fan of data-attributes or if you're planning a big website where you want a better and more flexible structure, take a look at skrollr-stylesheets.
Starting with 0.6.22 there's experimental AMD support. Please note that only skrollr core has AMD support so far. We will update the plugins in the future.
require(['skrollr'], function(skrollr){
skrollr.init();
});Being only able to define key frames in absolute values is simply insufficient for some cases. For example, if you don't know exactly where an element will be in the document. That's why there are two modes for key frames, namely absolute and relative mode.
The key frames are defined as absolute values describing how much the document has been scrolled down.
The syntax is data-[offset]-[anchor], where offset can be any integer (0 is default) and anchor can be either start (default) or end. Either offset or anchor can be omitted in some situations. Here are some examples of key frames and their meaning.
data-0=data-start=data-0-start: When the scroll top is 0.data-100=data-100-start: When the scroll top is 100.data--100=data--100-start: When the scroll top is -100 (sounds like nonsense, but keep in mind that interpolation will be relative to this point).data-end=data-0-end: When offset is 0, but counting from the bottom of the document instead of from the top. In short: when you reach the bottom of the page.data-100-end: 100px before we reach the bottom.data--100-end: 100px after we reach the bottom (again, it's up to you whether you need it).
Instead of defining key frames relative to the document (i.e. absolute), we are able to define them depending on the position of any element in relation to the viewport.
The syntax is data-[offset]-(viewport-anchor)-[element-anchor], where offset can again be any integer and defaults to 0. Both viewport-anchor (mandatory) and element-anchor (optional) can be one of top, center or bottom. If element-anchor is omitted, the value of viewport-anchor will be taken (just like with background-position). Here are some examples of key frames and their meaning.
data-top=data-0-top=data-top-top=data-0-top-top: When the element's top is aligned with the top of the viewport.data-100-top=data-100-top-top: When the element's top is 100px above the top of the viewport.data--100-top=data--100-top-top: When the element's top is 100px below the top of the viewport.data-top-bottom=data-0-top-bottom: When the bottom of the element is at the top of the viewport (it's just not visible).data-center-center=data-0-center-center: When the element is at the center of the viewport.data-bottom-center=data-0-bottom-center: When the element's center is at the bottom of the viewport, thus the upper half of the element is visible.
By default the keyframes are triggered by the position of the element where the keyframes are described. However there are times when the position of a second element should trigger the first element's keyframes. The data-anchor-target attribute can be used in these cases. The data-anchor-target attribute accepts any CSS selector and the position of the first element on the page matching the selector will be used to trigger keyframes on the element where the attribute is defined. data-anchor-target requires IE 8 or greater.
Examples: <div data-anchor-target="#foo"> will have it's keyframes tiggered by the position of the #foo element. Any CSS selector can be used, i.e data-anchor-target=".bar:not(.bacon) ~ span > a[href]"
Note: If you need to support IE 7, then you may only use IDs as anchor-targets, i.e. #foo. The IE plugin maps querySelector to getElementById.
Here's an infographic for better understanding of anchors (click to open PDF):
Important: All those values will be calculated up-front and transformed to absolute mode. So if either the element's box height changes (height, padding, border) or the elements position within the document, you probably need to call refresh() (see documentation in JavaScript section below). Window resizing is handled by skrollr.
All offsets shown above are given in absolute pixel values, e.g. data-300 for 300px from the top or data-13-top-bottom for a 13px offset to the top-bottom anchor. As of skrollr 0.6.13 you can also have offsets as percentages of the viewport by appending a p to the number. For example data-75p for when you scrolled down 75% of the viewport or data-10p-center to have a 10% offset from the center anchor.
Check out the skrollr-menu plugin.
I was lying to you. The syntax for absolute mode is not data-[offset]-[anchor] and for relative mode it's not data-[offset]-(viewport-anchor)-[element-anchor]. In both cases, offset can be preceded by a constant which can be passed to the init method. The name of the constant needs to be preceded with an underscore.
Example:
skrollr.init({
constants: {
foobar: 1337
}
});<div data-_foobar="left:0%;" data-_foobar--100="left:50%;" data-_foobar-100="left:100%;"></div>
<!--Equal to-->
<div data-1337="left:0%;" data-1237="left:50%;" data-1437="left:100%;"></div>Valid characters for a constant are [a-z0-9_].
Starting with skrollr 0.6.19 the word "constants" doesn't quite fit anymore, but who cares.
You can now use functions and percentages as constants. They are automatically evaluated when the window is resized or if you call refresh.
skrollr.init({
constants: {
foo: function() {
//Note: you can access the skrollr instance with `this` for things like `this.relativeToAbsolute`
return Math.random() * 100;//trolololol
},
vh: '100p'
}
});skrollr will add a skrollr class to the HTML element when calling init and will remove a no-skrollr class if present. Additionally, it will add a skrollr-desktop or skrollr-mobile class depending on which it detects. This allows fallback CSS rules to create a good user experience on unsupported devices or when JavaScript or skrollr are disabled.
All elements under skrollr's control (elements with appropriate data-attributes) will get the skrollable class. In addition, we add either the skrollable-before, skrollable-between or skrollable-after class, depending on whether the current scroll position is before, between or after the first/last (smallest/largest) keyframe of an element.
Starting with skrollr 0.6.24 you can also animate attribute and not just style properties. This is especially a big thing because in the SVG world many properties are implemented as attributes and not in CSS. Animating an attribute couldn't be simplier, just prefix the property with an @ symbol!
<polygon
points='426,720 -200,720 -200,0 955,0'
data-0="@points:426,720 -200,720 -200,0 955,0"
data-500="@points:380,720 -200,720 -200,0 1302,0">
</polygon>Note: as always, skrollr doesn't do any magic. It doesn't understand what a polygon or points are. It's only interpolating numbers, that's it. So make sure you have the same number of numbers in your keyframes (8 in this case).
Imagine the following animation
<div data-100="left:0%;" data-200="top:0%;" data-300="left:50%;" data-400="top:50%;"></div>One could expect left to have a value of 25% at keyframe 200. That is not the case. By design, skrollr only interpolates values between key frames which are direct neighbors. What actually happens is that skrollr internally fills out all holes once from left and then from right. So the above is equivalent to
<div data-100="left:0%;top:0%;" data-200="left:0%;top:0%;" data-300="left:50%;top:0%;" data-400="left:50%;top:50%;"></div>The reason why skrollr is so lightweight and powerful is because it literally interpolates every number it can find. If you want to prevent some side effect, you can suppress interpolation for a specific value by prepending an exclamation point.
Example:
<!-- This will get your image url f***** up because there's no "kitten1.4561799.jpg" and the like -->
<div data-0="background-image:url(kitten1.jpg);" data-100="background-image:url(kitten2.jpg)"></div>
<!-- Better -->
<div data-0="background-image:!url(kitten1.jpg);" data-100="background-image:!url(kitten2.jpg)"></div>Note: The values for both keyframes (if they contain a number) need to be prefixed if you want to avoid skrollr throwing an exception at you!
There are some limitations of skrollr you should be aware of.
- All numeric values have to have the same unit, even
0needs a unit. It's not possible to animate from5%to100px. skrollr won't complain, but results are undefined. - Animations between values which are composed of multiple numeric values like
margin:0 0 0 0;are only possible for the same number of values.margin:0px 0px 0px 0px;tomargin:0px 100px 50px 3px;is fine, but notmargin:10px;tomargin:5px 10px;. - Animations between CSS transforms only work when they use the same functions in same order. From
rotate(0deg) scale(1)torotate(1000deg) scale(5)is fine. - Color animations don't support named values like "red" or hex values like "#ff0000". Instead, you have to use
rgb(),rgba(),hsl()andhsla(). Don't worry, there's a skrollr plugin for IE < 9 to supporthsl()(without "a"!) and to fall rgba back to rgb. - Color animations only work for same color functions.
hsl()tohsl()orhsla()is fine, but notrgb()tohsl(). Which makes sense, because animating from the same colors in rgb space and in hsl space results in different animations (hsl gives you the nice rainbow stuff).
But feel free to send in a pull request to fix any of them. Just keep in mind that keeping skrollr as lightweight as possible has high priority.
On the JavaScript part there's not much to do (you can, if you want to!). So if you only know CSS and HTML, perfect.
All there is to do is to call skrollr.init([options]); which returns an instance of the singleton skrollr class. Subsequent calls to init() will just return the same skrollr instance again.
Possible options for init() are
Smooth scrolling smoothens your animations. When you scroll down 50 pixels, the animations will transition instead of jumping to the new position.
The Smooth Scrolling speed.
The document element
The actual scrolling element (Required when using smoothScroll)
An object containing integers as values. The keys can contain [a-z0-9_]. They do not need a leading underscore.
Example: data-_myconst-200 and skrollr.init({constants: {myconst: 300}}) result in data-500.
By default, skrollr uses the largest key frame and makes document height + viewport height this high, thus the max possible scroll top offset. If your animation runs too fast or too slow, just adjust the scale value.
scale only affects keyframes in absolute mode.
When forceHeight is set to false, scale is ignored.
scale affects constants as well.
scale does only affect key frames in absolute mode, e.g. data-500 but not data-top.
true: Make sure the document is high enough that all key frames fit inside. Example: You use data-1000, but the content only makes the document 500px high. skrollr will ensure that you can scroll down the whole 1000px. Or if you use relative mode, e.g. data-top-bottom, skrollr will make sure the bottom of the element can actually reach the top of the viewport.
false: Don't manipulate the document and just keep the natural scrollbar.
This option specifies how to handle animations when the scroll position is outside the range on the keyframes (i.e. before the first or after the last keyframe).
One of three options are possible
set(default): When before/after the first/last keyframe, apply the styles of the first/last keyframe to the element.ease: Same as set, but the values will be transformed using the given easing function.reset: When before/after the first/last keyframe, apply the styles which the element had before skrollr did anything. This means resetting the class attribute as well as removing all styles which have been applied to thestyleproperty. This means the element won't have anyskrollable-*CSS classes.
Example:
Given the following element with two keyframes
<div data-1000="left:0%;top:0%;" data-2000="left:50%;top:100%;" style="left:-100%;" class="section"></div>and the following easing function which always returns 0.5 (I know it's pointless, but it's just an example. A real world example would be an easing function that represents a curve and starts somewhere between 0 and 1, but not at 1)
function(p) {
return 0.5;
}and imagine the scrollbar is at 237, which is below the first keyframe which is at 1000.
setwill result in<div style="left:0%;top:0%;" class="section skrollable skrollable-before"></div>which is plaindata-1000.easewill result in<div style="left:25%;top:50%;" class="section skrollable skrollable-before"></div>which is0.5 * data-1000.resetwill result in<div style="left:-100%;" class="section"></div>which is what the element originally had. Note howtopis missing.
A listener function that gets called each time right before we render everything. The function will be passed an object with the following properties:
{
curTop: 10, //the current scroll top offset
lastTop: 0, //the top value of last time
maxTop: 100, //the max value you can scroll to. curTop/maxTop will give you the current progress.
direction: 'down' //either up or down
}Returning false will prevent rendering.
A listener function that gets called right after we finished rendering everything. The function will be passed with the same parameters as beforerender.
Example
skrollr.init({
render: function(data) {
//Log the current scroll position.
console.log(data.curTop);
}
});Experimental
In order to receive keyframe events from an element, add the data-emit-events attribute to the element. The keyframe function will be called with three arguments
- The
elementthat passed the keyframe. - The
nameof the keyframe, camel-cased (see example). - The
directionthe user is scrolling.
Example:
<div
data-500="..."
data-top-bottom="..."
data-_offset-center="..."
data-emit-events
>
Some content
</div>skrollr.init({
keyframe: function(element, name, direction) {
//name will be one of data500, dataTopBottom, data_offsetCenter
}
});Note: this is experimental, expect the API to change! Originally I wanted to emit the events right on the element, so you could do this
//Wouldn't this be nice?
document.querySelector('#foo').addEventListener('skrollr.dataTopBottom.up', function() {
//#foo just passed the data-top-bottom keyframe while scrolling up
}, false)but IE.
An object defining new easing functions or overwriting existing ones. Easing functions get just one argument, which is a value between 0 and 1 (the percentage of how much of the animation is done). The function should return a value between 0 and 1 as well, but for some easings a value less than 0 or greater than 1 is just fine.
An easing function basically transforms the timeline for an animation. When the animation should be 50% done, you can transform it to be 90% done or whatever your function does.
Example:
skrollr.init({
easing: {
//This easing will sure drive you crazy
wtf: Math.random,
inverted: function(p) {
return 1 - p;
}
}
});You can now use the easing functions like any other.
skrollr ships with some built in functions:
- linear: The default. Doesn't need to be specified.
- quadratic: To the power of two. So 50% looks like 25%.
- cubic: To the power of three. So 50% looks like 12.5%
- begin/end: They always return 0 or 1 respectively. No animation.
- swing: Slow at the beginning and accelerates at the end. So 25% -> 14.6%, 50% -> 50%, 75% -> 85.3%
- sqrt: Square root. Starts fast, slows down at the end.
- outCubic
- bounce: Bounces like a ball. See https://www.desmos.com/calculator/tbr20s8vd2 for a graphical representation.
Custom easing
- Use this generator
- Insert the given polynomial coeficients instead of t, t2, t3, t4 and t5
t5*(p*p*p*p*p) + t4*(p*p*p*p) + t3*(p*p*p) + t2*(p*p) + t*p
Example shown with the values for easeOutElasticBig
easeOutElasticBig: function(p) {
return 56*(p*p*p*p*p) - 175*(p*p*p*p) + 200*(p*p*p) - 100*(p*p) + 20*p;
}
Returns the skrollr instance if init() has been called before or undefined.
Calling init() returns an instance of skrollr which exposes a public api.
Reparses all given elements. You can pass a single element or an array-like element (Array, NodeList or jQuery object)
Useful when
- Elements in
relativemode change and need to be updated. - Data-attributes are manipulated dynamically.
- New elements are added to the DOM and should be controlled by skrollr.
When no elements are given, all elements in the document will be parsed again. In fact, when calling skrollr.init() skrollr uses refresh() without parameters internally.
Time consuming operations, should not be called on every rendering.
Returns an integer which represents the absolute scroll position which correlates to the relative anchor.
element must be a DOM element.
viewportAnchor and elementAnchor must be one of top, center or bottom
Example:
var offset = s.relativeToAbsolute(document.getElementById('foo'), 'top', 'bottom');
//offset contains the scroll position at which #foo's bottom is at the top of the viewport.
//If you now use setScrollTop(offset) or animateTo(offset) #foo's bottom will be perfectly aligned with the top of the viewport. Yay.Returns the current scroll offset in pixels. Normalizes different browser quirks and handles mobile scrolling.
Returns the number of pixels that can be scrolled down in total. If forceHeight is true, that's usually the largest keyframe. Otherwise it's the height of the document minus the viewport height.
Sets the top offset using window.scrollTo(0, top) on desktop or updating the internal state in case of mobile scrolling.
When force is set to true, skrollr will jump to the new position without any kind of transition. By default, the global smoothScrolling setting applies.
Returns if skrollr runs in mobile mode (see also mobileCheck option).
Animates the scroll position from current position to top. Possible options are
How long the animation should run in milliseconds. The default is 1000 or one second.
The name of an easing function. The same functions can be used as for property animations. Default is linear .
A function to be called after the animation finished. When you pass a top value, which is the same as the current, then the function will be called immediately. The function gets a boolean argument interrupted which indicates if the animation was interrupted by stopAnimateTo or finished to the end.
Stops the animation and calls the done callback passing true as interrupted arguments.
Returns if an animation caused by animateTo is running.
Set a listener function for one of the events described in the options section (beforerender, render, keyframe). Only one listener can be attached at a given time. This method overwrites the current listener, if any.
Removes the listener for the given event.
Destroys skrollr. All class and style attributes will be set to the values they had before.
See HISTORY.md.