26 January 2012

Free Javascript for Rotating Website Banner or Fading Slideshow - standalone

As flash becomes less widespread I've had more and more instances where I need to create website banners in Javascript rather than my old flash approach. Today I've decided to share my method with my adoring public (that's you!).

This method is completely standalone and does not require jQuery or any other plugin or library. It has been tested and works in latest versions of all browsers.

View a demo here (right click to get the whole source at once) or view the step-by-step instructions below...

Please see my note before copying my code - thank you! >

Add this between your head tags. You can tweak the speeds etc in the BANNER SETUP section at the top.

//ROTATING BANNER BY CIARAN O'KELLY 2012 - BLOG.CRONDESIGN.COM

//BANNER SETUP:
var imageCount = 5;  //how many images in total?
var changeSpeed = 3;  //how many seconds between fades?
var fadeSpeed = 0.5; //how many seconds should the fade take?
var fps = 25;  //animation frames per second

//BANNER FUNCTIONS:
var topImgID
var changeInterval

function $(id){ //just a shortcut function:
 return(document.getElementById(id));
}

function changeOpac(obj, opacity) {//change the opacity for different browsers:
 obj = obj.style; 
 obj.opacity = (opacity / 100);
 obj.MozOpacity = (opacity / 100);
 obj.KhtmlOpacity = (opacity / 100);
 obj.filter = "alpha(opacity=" + opacity + ")";
}

function changeImage(){
 var nextImgID = ( topImgID+1 <= imageCount ? topImgID+1 : 1 ); //get id number of next image in list
 var nextImg = $('banner'+nextImgID);
 var lastImg = $('banner'+topImgID);
 var opac = 0;
 changeOpac( nextImg, opac) //make next image invisible, then bring it to the top:
 lastImg.style.zIndex = 2;
 nextImg.style.zIndex = 3;

 var fadeInterval = setInterval(function(){ //run fade on interval:
  if(opac < 100){//continue fade:
   opac += Math.ceil(100/(fadeSpeed*fps));
   changeOpac(nextImg, opac);
  }else{//end fade:
   lastImg.style.zIndex = 1;
   clearInterval(fadeInterval);
  }
 }, 1000/fps)

 topImgID = nextImgID; //prepare next fade
}

function startBanner(firstImageID){
 topImgID = (firstImageID==undefined ? 1+Math.floor(Math.random()*(imageCount)) : firstImageID);
 $('banner'+topImgID).style.zIndex = 2;
 changeInterval = setInterval(changeImage, changeSpeed*1000);
}
Add this to your stylesheet and tweak to your liking:

.banner{position:absolute; z-index:1; height:230px; width:720px; top:0px; background:#FFF; border:solid 1px #CCC}
.banner h1{position: absolute; bottom:20px; right:20px; font-style:italic; color:#444; float:right; width:50%; font-size:40px; text-align:right; line-height:100%;}
#banner1{background-image:url(banner1.jpg);}
#banner2{background-image:url(banner2.jpg);}
#banner3{background:#F90}
#banner4{background:#FFC}
#banner5{background:#99CCFF}
Add this to your html and tweak to your liking:

<div id="banner2" class="banner">
    <h1>It runs on a loop</h1>
</div>
<div id="banner3" class="banner">
    <h1>The images are actually div tags</h1>
</div>
<div id="banner4" class="banner">
    <h1>So they can contain text, colours or other content</h1>
</div>
<div id="banner5" class="banner">
    <h1>You can control the speed, the start image & number of images</h1>
</div>
<div id="banner1" class="banner">
    <h1>This banner fades between images</h1>
</div>
Finally, if you want the banner to automatically start, add this to your body tag. 1 is the id of the first image you want to show. Leave it blank to choose a random image.

<body onload="startBanner(1)">

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