Part 1
Intro
I haven’t posted much lately. I’ve been tied up creating this folder browser using client-side JavaScript. I probably made every mistake in the book, but I worked through them all and the outcome is pretty cool, if I say so myself! It works in IE, FireFox and even Blackberry!
The details
I broke down the development of this browse app into 12 stages. Given time, I might show the progression of my thinking as each version becomes closer and closer to fulfilling all initial objectives. But who has time? I’ll show the source for browse3.html, warts and all, and then skip many iterations and jump to showing the final source, browse12.html.
Browse3.html
It ain’t pretty. It isn’t even correct. But it “does stuff.” It assumes Apache web server is running and “borrows” the closed and open folder icons from apache’s /icons directory. In my case I have a top-level directory called /homepic with folders under that and sub-folders under those folders that I want the ability to browse and , ultimately, take some action such as displaying all the folder’s images in the image viewer I wrote earlier.
<!DOCTYPE html>
<html>
<head>
<script type="text/javascript">
// global object
var folder = new Object;
function displayDate()
{
document.getElementById("demo").innerHTML=Date();
}
function init() {
// big initialization - generated code from perl perusal of directories
// see http://www.quirksmode.org/js/associative.html
// var folder = new Object;
// we need this empty assignment to extend object with subproperties later on
folder['homepic'] = '/homepic';
//folder['/homepic'].path = '/homepic';
folder.homepic.state = 'closed';
folder[0] = '/homepic/kodak_pictures';
folder[1] = '/homepic/pictures_chronological';
folder['/homepic/kodak_pictures'] = '/homepic/kodak_pictures';
folder['/homepic/kodak_pictures'].state = 'closed';
//folder['/homepic/kodak_pictures'].path = '/homepic/kodak_pictures';
folder['/homepic/pictures_chronological'] = '/homepic/pictures_chronological';
folder['/homepic/pictures_chronological'].state = 'closed';
//folder['/homepic/pictures_chronological'].path = '/homepic/pictures_chronological';
var child = 'homepic';
var cstate = folder['homepic'].state;
var cpath = folder[0];
}
function browse(f) {
document.getElementById("demo").innerHTML="folder: "+f+" ";
var icon;
var imgid;
var fname;
if (f == "browse") {
// see http://www.quirksmode.org/dom/intro.html#create
// one-time initialization
init();
document.getElementById("browse").innerHTML='';
icon = document.createElement('IMG');
icon.src = "/icons/folder.gif";
icon.id = "icon-/homepic";
icon.onclick = Function('browse("/homepic")');
document.getElementById("browse").appendChild(icon);
var divfolder = document.createElement('DIV');
divfolder.id = "/homepic";
document.getElementById("browse").appendChild(divfolder);
var x = document.createTextNode('homepic');
document.getElementById('/homepic').appendChild(x);
//document.getElementById("browse").innerHTML='<img id="homepic" onclick="browse(\'homepic\')" src="/icons/folder.gif">ho
mepic<br>';
} else {
imgid = 'icon-' + f;
// change img to one of open folder
document.getElementById(imgid).src = "/icons/folder.open.gif";
// nope? imgid.src = "/icons/folder.open.gif";
for (i=0;i<3;i++) {
icon = document.createElement('IMG');
icon.src = "/icons/folder.gif";
fname = folder[f].children[i];
//fname = folder['homepic'].children[i];
icon.id = "icon-" + fname;
icon.onclick = Function('browse('+fname+')');
document.getElementById(f).appendChild(icon);
var divfolder = document.createElement('DIV');
divfolder.id = fname;
document.getElementById(f).appendChild(divfolder);
var x = document.createTextNode(fname);
document.getElementById(f).appendChild(x);
} // end loop over children
}
}
// note variable # or arguments are being passed
function openfolder()
{
var f = arguments[0];
var dir = "/icons/";
var fopen = "folder.open.gif";
var fclosed = "folder.gif";
var folder = document.getElementById(f);
var ftype = folder.src;
// src includes http... Get rid of stuff in front
var patt = /.*(folder.+)/;
var ftypebare = ftype.replace(patt,"$1");
// for debugging
document.getElementById("demo").innerHTML="folder: "+f+" "+ftypebare;
if (ftypebare == fopen) {
// close folder and remove sub-folders
folder.src = dir+fclosed;
document.getElementById("homepic/pictures_chronological").innerHTML='';
} else {
// open up folder and reveal sub-folders
folder.src = dir+fopen;
for (var i = 0; i < arguments.length; i++) {
var placeid = arguments[i];
var srcid = '/' + placeid;
document.getElementById(placeid).innerHTML=' <img id="' + srcid + '" onclick="openfolder(\'pictures_ch
ronological\')" src="/icons/folder.gif"/> pictures_chronological<br>';
}
}
}
</script>
</head>
<body>
<h1>Folder Browser</h1>
<p id="demo">Debug Aid.</p>
<p id="browse"><a href="#" onclick='browse("browse")'>Folder Browser</a></p>
<img id="homepic" onclick="openfolder('homepic','homepic/pictures_chronological','homepic/canon_pictures')" src="/icons/fol
der.gif"/> homepic<br>
<div id="homepic/pictures_chronological"></div>
<div id="homepic/canon_pictures"></div>
<img id="cfolder2" onclick="openfolder(2)" src="/icons/folder.gif"/><br>
<img id="cfolder3" onclick="openfolder(3)" src="/icons/folder.gif"/><br>
<img id="cfolder4" onclick="openfolder(4)" src="/icons/folder.gif"/><br>
</body>
</html> |
So you see in browse3 I’m wrestling with how to work with JavaScript Objects (which I didn’t really know existed at that time). I badly wanted to give an associative array properties, as in the initialization line
folder['/homepic/kodak_pictures'].state = 'closed'; |
but I couldn’t find any examples on the Internet. I eventually learned that wasn’t a correct assignment.
So one of my biggest and most worthwhile lessons was to gain a decent understanding of JavaScript objects, which hold multiple values, and object properties.
I tried to use Firebug for Firefox, with very limited success, but at least I could step through the Javascript code and see which branch in a conditional was being executed compared to what I thought should be executed, which tipped me off to one vexing problem concerning opening and closing folders multiple times. Also just looking up the error in Internet Explorer by double-=clicking the warning sign in the corner was tremendously helpful.
So…skipping for now versions 4 – 11, we arrive at browse12.html:
Browse12.html
<!DOCTYPE html>
<html>
<head>
<script type="text/javascript">
// global object
var folder = new Object;
function displayDate()
{
document.getElementById("demo").innerHTML=Date();
}
function init() {
// big initialization - generated code from perl perusal of directories
// I think my big breakthrough was to learn about Javascript objects and their properties
// from the book Javascript The Definitive Guide, 5th edition by D.Flanagan
// Some additional inspiration came from http://www.quirksmode.org/dom/intro.html#create
// folder is an associative array with properties path, state,depth and kids (which is itself an array)
// first entry is initial top-level to get things started
folder['browse'] = {path:'',depth:0,kids:['homepic']};
// regular entries:
folder['/homepic'] = {path:'/homepic',depth:1,kids:['kodak_pictures','pictures_chronological']};
// values for sub-folders
// /homepic/kodak_pictures
folder['/homepic/kodak_pictures'] = {path:'/homepic/kodak_pictures',depth:2,kids:['2002_05','2002_06']};
// /homepic/pictures_chronological
folder['/homepic/pictures_chronological'] = {path:'/homepic/pictures_chronological',depth:2,kids:['2011_11','2011_12']};
}
function browse(f) {
document.getElementById("demo").innerHTML="folder: "+f+" ";
var icon;
var imgid;
var fname;
var table;
if (f == "browse") {
// one-time initialization
init();
}
imgid = 'icon-' + f;
if (!folder[f]) {
// folder not defined: must be a terminal folder. Do something here eventually
// but for now do nothing whatsoever
} else {
if (folder[f].state === undefined || folder[f].state == 'closed') {
// change img to one of open folder
if (f == 'browse') {
document.getElementById(f).innerHTML='';
} else {
document.getElementById(imgid).src = "/icons/folder.open.gif";
}
var kids = folder[f].kids;
for(var i=0; i < kids.length; i++) {
table = document.createElement("table");
table.border = 0;
var row = document.createElement("tr");
var td1 = document.createElement("td");
var td2 = document.createElement("td");
var td3 = document.createElement("td");
icon = document.createElement("img");
icon.src = "/icons/folder.gif";
if (f == "browse") {
fname = "/" + kids[i];
} else {
fname = f + "/" + kids[i];
}
icon.id = "icon-" + fname;
if (folder[fname])
folder[fname].state = 'closed';
icon.onclick = Function('browse("'+fname+'")');
td1.width = 27 + folder[folder].depth*27;
td1.align = "right";
td1.appendChild(icon);
var node = document.createTextNode(kids[i]);
td3.appendChild(node);
row.appendChild(td1); row.appendChild(td2); row.appendChild(td3);
table.appendChild(row);
document.getElementById(f).appendChild(table);
var divfolder = document.createElement("div");
divfolder.id = fname;
document.getElementById(f).appendChild(divfolder);
folder[f].state = 'open';
} // end loop over children
} else {
// set folder to closed state
// this innerHTML nullification is kind of a kludge, but it works
document.getElementById(f).innerHTML='';
document.getElementById(imgid).src = "/icons/folder.gif";
folder[f].state = 'closed';
} // end conditional over folder state
} // end condition over whether folder is defined or not
} // end function browse
</script>
</head>
<body>
<h1>Folder Browser</h1>
<p id="demo">Debug Aid.</p>
<p id="browse"><a href="#" onclick='browse("browse")'>Folder Browser</a></p>
</body>
</html> |
That’s it! Not bad, huh? I pan to generate the init() function periodically and automatically from a Perl script which peruses my directories.
I could have used Ajax and generated the subfolder information on the fly as it is needed – not that I know how, I just know enough to know it is possible and therefore I could do it – but I thought this method of pre-loading all the information might be a little more efficient. If this were a folder and file browser it would be different, but for now it is just a folder browser.
So the main revelation is that I had to set my associative array members to be objects during initialization, as in
folder['/homepic'] = {path:'/homepic',depth:1,kids:['kodak_pictures','pictures_chronological']}; |
and one of the object values is itself an anonymous array that holds the sub-folders.
Buying an actual book was probably a good move. I went with JavaScript, The Definitive Guide, 5th edition. Note that this is not the latest edition – the 6th – but this way I could buy the book used for a lot less and not get myself further confused by HTML5, which I am not ready to tackle and which many browsers do not yet fully support. The book is pretty heavy going and the discussion of DOM was particularly difficult and the examples too few and too removed from the real world. But the Core Javascript discussion made a lot of sense to me so was by itself worth the purchase price.
In my next post I’ve posted the Perl script which can generate the folder object initialization.
Part 2, A simple Perl script to build JavaScript folder objects
Conclusion
In this part one of a two-part post I’ve provided the JavaScript that implements a very compact folder browser. It has been tested on both IE and Firefox. The 2nd part of this series will provide the Perl Jvascript code generator for automation of the object creation.