special attributes in tag that are processed by javascript file - html

Question

Impress.js supports a number of attributes:
data-x, data-y, data-z will move the slide on the screen in 3D space;
data-rotate, data-rotate-x, data-rotate-y rotate the element around the specified axis (in degrees);
data-scale – enlarges or shrinks the slide.
div id="intro" class="step" data-x="0" data-y="0">
<h2>Introducing Galaxy Nexus</h2>
<p>Android 4.0<br /> Super Amoled 720p Screen<br />
<img src="assets/img/nexus_1.jpg" width="232" height="458" alt="Galaxy Nexus" />
<!-- We are offsetting the second slide, rotating it and making it 1.8 times larger -->
<div id="simplicity" class="step" data-x="1100" data-y="1200" data-scale="1.8" data-rotate="190">
<h2>Simplicity in Android 4.0</h2>
<p>Android 4.0, Ice Cream Sandwich brings an entirely new look and feel..</p>
<img src="assets/img/nexus_2.jpg" width="289" height="535" alt="Galaxy Nexus" />
Impress.js
(function ( document, window ) {
'use strict';
// HELPER FUNCTIONS
var pfx = (function () {
var style = document.createElement('dummy').style,
prefixes = 'Webkit Moz O ms Khtml'.split(' '),
memory = {};
return function ( prop ) {
if ( typeof memory[ prop ] === "undefined" ) {
var ucProp = prop.charAt(0).toUpperCase() + prop.substr(1),
props = (prop + ' ' + prefixes.join(ucProp + ' ') + ucProp).split(' ');
memory[ prop ] = null;
for ( var i in props ) {
if ( style[ props[i] ] !== undefined ) {
memory[ prop ] = props[i];
break;
}
}
}
return memory[ prop ];
}
})();
var arrayify = function ( a ) {
return [].slice.call( a );
};
var css = function ( el, props ) {
var key, pkey;
for ( key in props ) {
if ( props.hasOwnProperty(key) ) {
pkey = pfx(key);
if ( pkey != null ) {
el.style[pkey] = props[key];
}
}
}
return el;
}
var byId = function ( id ) {
return document.getElementById(id);
}
var $ = function ( selector, context ) {
context = context || document;
return context.querySelector(selector);
};
var $$ = function ( selector, context ) {
context = context || document;
return arrayify( context.querySelectorAll(selector) );
};
var translate = function ( t ) {
return " translate3d(" + t.x + "px," + t.y + "px," + t.z + "px) ";
};
var rotate = function ( r, revert ) {
var rX = " rotateX(" + r.x + "deg) ",
rY = " rotateY(" + r.y + "deg) ",
rZ = " rotateZ(" + r.z + "deg) ";
return revert ? rZ+rY+rX : rX+rY+rZ;
};
var scale = function ( s ) {
return " scale(" + s + ") ";
};
var getElementFromUrl = function () {
// get id from url # by removing `#` or `#/` from the beginning,
// so both "fallback" `#slide-id` and "enhanced" `#/slide-id` will work
return byId( window.location.hash.replace(/^#\/?/,"") );
};
// CHECK SUPPORT
var ua = navigator.userAgent.toLowerCase();
var impressSupported = ( pfx("perspective") != null ) &&
( document.body.classList ) &&
( document.body.dataset ) &&
( ua.search(/(iphone)|(ipod)|(android)/) == -1 );
var roots = {};
var impress = window.impress = function ( rootId ) {
rootId = rootId || "impress";
// if already initialized just return the API
if (roots["impress-root-" + rootId]) {
return roots["impress-root-" + rootId];
}
// DOM ELEMENTS
var root = byId( rootId );
if (!impressSupported) {
root.className = "impress-not-supported";
return;
} else {
root.className = "";
}
// viewport updates for iPad
var meta = $("meta[name='viewport']") || document.createElement("meta");
// hardcoding these values looks pretty bad, as they kind of depend on the content
// so they should be at least configurable
meta.content = "width=1024, minimum-scale=0.75, maximum-scale=0.75, user-scalable=no";
if (meta.parentNode != document.head) {
meta.name = 'viewport';
document.head.appendChild(meta);
}
var canvas = document.createElement("div");
canvas.className = "canvas";
arrayify( root.childNodes ).forEach(function ( el ) {
canvas.appendChild( el );
});
root.appendChild(canvas);
var steps = $$(".step", root);
// SETUP
// set initial values and defaults
document.documentElement.style.height = "100%";
css(document.body, {
height: "100%",
overflow: "hidden"
});
var props = {
position: "absolute",
transformOrigin: "top left",
transition: "all 0s ease-in-out",
transformStyle: "preserve-3d"
}
css(root, props);
css(root, {
top: "50%",
left: "50%",
perspective: "1000px"
});
css(canvas, props);
var current = {
translate: { x: 0, y: 0, z: 0 },
rotate: { x: 0, y: 0, z: 0 },
scale: 1
};
var stepData = {};
var isStep = function ( el ) {
return !!(el && el.id && stepData["impress-" + el.id]);
}
steps.forEach(function ( el, idx ) {
var data = el.dataset,
step = {
translate: {
x: data.x || 0,
y: data.y || 0,
z: data.z || 0
},
rotate: {
x: data.rotateX || 0,
y: data.rotateY || 0,
z: data.rotateZ || data.rotate || 0
},
scale: data.scale || 1,
el: el
};
if ( !el.id ) {
el.id = "step-" + (idx + 1);
}
stepData["impress-" + el.id] = step;
css(el, {
position: "absolute",
transform: "translate(-50%,-50%)" +
translate(step.translate) +
rotate(step.rotate) +
scale(step.scale),
transformStyle: "preserve-3d"
});
});
// making given step active
var active = null;
var hashTimeout = null;
var goto = function ( el ) {
if ( !isStep(el) || el == active) {
// selected element is not defined as step or is already active
return false;
}
// Sometimes it's possible to trigger focus on first link with some keyboard action.
// Browser in such a case tries to scroll the page to make this element visible
// (even that body overflow is set to hidden) and it breaks our careful positioning.
//
// So, as a lousy (and lazy) workaround we will make the page scroll back to the top
// whenever slide is selected
//
// If you are reading this and know any better way to handle it, I'll be glad to hear about it!
window.scrollTo(0, 0);
var step = stepData["impress-" + el.id];
if ( active ) {
active.classList.remove("active");
}
el.classList.add("active");
root.className = "step-" + el.id;
// `#/step-id` is used instead of `#step-id` to prevent default browser
// scrolling to element in hash
//
// and it has to be set after animation finishes, because in chrome it
// causes transtion being laggy
window.clearTimeout( hashTimeout );
hashTimeout = window.setTimeout(function () {
window.location.hash = "#/" + el.id;
}, 1000);
var target = {
rotate: {
x: -parseInt(step.rotate.x, 10),
y: -parseInt(step.rotate.y, 10),
z: -parseInt(step.rotate.z, 10)
},
translate: {
x: -step.translate.x,
y: -step.translate.y,
z: -step.translate.z
},
scale: 1 / parseFloat(step.scale)
};
// check if the transition is zooming in or not
var zoomin = target.scale >= current.scale;
// if presentation starts (nothing is active yet)
// don't animate (set duration to 0)
var duration = (active) ? "1s" : "0";
css(root, {
// to keep the perspective look similar for different scales
// we need to 'scale' the perspective, too
perspective: step.scale * 1000 + "px",
transform: scale(target.scale),
transitionDuration: duration,
transitionDelay: (zoomin ? "500ms" : "0ms")
});
css(canvas, {
transform: rotate(target.rotate, true) + translate(target.translate),
transitionDuration: duration,
transitionDelay: (zoomin ? "0ms" : "500ms")
});
current = target;
active = el;
return el;
};
var prev = function () {
var prev = steps.indexOf( active ) - 1;
prev = prev >= 0 ? steps[ prev ] : steps[ steps.length-1 ];
return goto(prev);
};
var next = function () {
var next = steps.indexOf( active ) + 1;
next = next < steps.length ? steps[ next ] : steps[ 0 ];
return goto(next);
};
window.addEventListener("hashchange", function () {
goto( getElementFromUrl() );
}, false);
window.addEventListener("orientationchange", function () {
window.scrollTo(0, 0);
}, false);
// START
// by selecting step defined in url or first step of the presentation
goto(getElementFromUrl() || steps[0]);
return (roots[ "impress-root-" + rootId ] = {
goto: goto,
next: next,
prev: prev
});
}
})(document, window);
// EVENTS
(function ( document, window ) {
'use strict';
// keyboard navigation handler
document.addEventListener("keydown", function ( event ) {
if ( event.keyCode == 9 || ( event.keyCode >= 32 && event.keyCode <= 34 ) || (event.keyCode >= 37 && event.keyCode <= 40) ) {
switch( event.keyCode ) {
case 33: ; // pg up
case 37: ; // left
case 38: // up
impress().prev();
break;
case 9: ; // tab
case 32: ; // space
case 34: ; // pg down
case 39: ; // right
case 40: // down
impress().next();
break;
}
event.preventDefault();
}
}, false);
// delegated handler for clicking on the links to presentation steps
document.addEventListener("click", function ( event ) {
// event delegation with "bubbling"
// check if event target (or any of its parents is a link)
var target = event.target;
while ( (target.tagName != "A") &&
(target != document.body) ) {
target = target.parentNode;
}
if ( target.tagName == "A" ) {
var href = target.getAttribute("href");
// if it's a link to presentation step, target this step
if ( href && href[0] == '#' ) {
target = document.getElementById( href.slice(1) );
}
}
if ( impress().goto(target) ) {
event.stopImmediatePropagation();
event.preventDefault();
}
}, false);
// delegated handler for clicking on step elements
document.addEventListener("click", function ( event ) {
var target = event.target;
// find closest step element
while ( !target.classList.contains("step") &&
(target != document.body) ) {
target = target.parentNode;
}
if ( impress().goto(target) ) {
event.preventDefault();
}
}, false);
// touch handler to detect taps on the left and right side of the screen
document.addEventListener("touchstart", function ( event ) {
if (event.touches.length === 1) {
var x = event.touches[0].clientX,
width = window.innerWidth * 0.3,
result = null;
if ( x < width ) {
result = impress().prev();
} else if ( x > window.innerWidth - width ) {
result = impress().next();
}
if (result) {
event.preventDefault();
}
}
}, false);
})(document, window);
My question is the Impress.js supposedly to process the data-x, data-y, data-scale attribute of the div tag. But I don't see where the code in Impress.js is doing that. Can someone point it out?

Answer 1

This intro to datasets may help.
First this part checking support for .dataset:
// CHECK SUPPORT
var ua = navigator.userAgent.toLowerCase();
var impressSupported = ( pfx("perspective") != null ) &&
( document.body.classList ) &&
( document.body.dataset ) &&
( ua.search(/(iphone)|(ipod)|(android)/) == -1 );
Then this part of the code, about halfway down:
steps.forEach(function ( el, idx ) {
var data = el.dataset,
step = {
translate: {
x: data.x || 0,
y: data.y || 0,
z: data.z || 0
},
rotate: {
x: data.rotateX || 0,
y: data.rotateY || 0,
z: data.rotateZ || data.rotate || 0
},
scale: data.scale || 1,
el: el
};