AJAX : A Basic Example and a Bookmarklet
Okay now what you all been waiting for: my example on AJAX. Waring: I am not going to go into extreme detail; you can get Dave Crane’s and my book (AJAX in Action) for that when it comes out later this year. First lets see an example of AJAX working right here under our noses.
Now everyone in a JavaScript world says. How can I protect my pages with a username and password without a server side language? Well it can not be done, but you can make it hard to find your content. In this example below you can see a textbox, a password box and the wonderful submit button. Try entering in a username and password.
Look at the source and you will see there is no username and password. Instead we are using the username and password field to see if the file exists. With AJAX, we look to see if this file is there. If it is, we go there, if not we get the error. Well I am sure you want to see the location so the username is Eric and the password is pass. Now you are able to go there and see my message.
So what is the code to do this? Well now we all know the fun we have coding JavaScript, nothing works the same for different browsers. With IE we need to use ActiveX to do it. Mozilla has there own method to do it.
First we have two things. We have the code that does the request, and then we have a function that handles the returned data. If you are using one of those libraries, you may not have seen this, so open up your eyes wide. Now I am just going to explain the code with comments. (Yeah that is cheating compared to my normal discussion style here on my blog, but I am trying to write a book you know!)
<html>
<head>
<script type="text/javascript">
//We need a wonderful global variables to hold our request object!
//So we can pass it around.
var reqXML;
//We need to have a global variable to hold the url.
//It keeps us from having to repeat code!
var url;
//Create our function to start the request
function VerifyLogin(){
//inform there is an action!
document.getElementById("spanLog").innerHTML = "<span style='color:green'> Checking Information</span>";
//Grab our form field values
var strName = document.Form1.username.value;
var strPass = document.Form1.password.value;
//Make the URL for the request
url = "http://radio.javaranch.com/pascarello/files/" + strName + strPass + ".html";
//determine if the browser is Moz, FF, NN, Op
if (window.XMLHttpRequest){
reqXML = new XMLHttpRequest(); //set the request
reqXML.onreadystatechange = LoginUser; //function to call on each set
reqXML.open("GET", url, true); //set the page to request
reqXML.send(null); //initialize the request
}
//ActiveX - can we say IE?
else if(window.ActiveXObject){
//Create our RequestObject
reqXML = new ActiveXObject("Microsoft.XMLHTTP");
if(reqXML){
reqXML.onreadystatechange = LoginUser //function to call on each step
reqXML.open("GET", url, true); //set the page to request
reqXML.send(null); //initialize the request
}
}
else{ //I do not support this so I need to do something!
window.location.href = url;
}
}
function LoginUser(){
//Look to see if the request is in the 4th stage (complete)
if(reqXML.readyState == 4){
//Make sure that we get a sucess page status
if(reqXML.status == 200){
//change our location
window.location.href = url;
}
//For all of the wrong error pages here
else{
document.getElementById("spanLog").innerHTML = "<span style='color:red'> Error: username and password is not correct!</span>";
}
}
}
</script>
</head>
<body>
<form name="Form1" onsubmit="VerifyLogin();return false;">
<span style="font-family:courier">User Name: </span><input type="text" name="username"><br/>
<span style="font-family:courier">Password: </span><input type="password" name="password"><br/>
<input type="submit" name="btnSub" value="Login" style="font-family:courier">
</form>
</body>
</html>
Now I added the event handler to the form to allow us to submit it, I did not think that needed a comment! Now you may be wondering what some things actually mean.
Now the XMLHttpRequest Object has an event handler onreadystatechange that we set to call LoginUser. Now when the XMLHttpRequest is executed we go through 5 stages:
- 0 - un-initialized
- 1 - loading
- 2 - loaded
- 3 - interactive
- 4 - complete
We also need to check the status of the document that has been returned. We are looking for a status code of 200 since that means success! We do not want to see that 404 error!
I know I just went over this fast, but you can get more details in AJAX in Action when it comes out. But you may be saying why would I ever want to use this? Well with some minor changes, creating a JS file, and creating a bookmarklet, we can make a very very very very (did I say very) useful tool for a web master that has to check pages to see if all of the links are correct.
Let’s try this out then I will give you the source code. The first step is create a bookmarklet. Take the link below, right click on it, and save it as a bookmark. Agree to the security warning because the link is a JavaScript statement that executes some code. You will be shown the code for the bookmark on the example page.
After you bookmarked that link above, you need to do open up this link below, go to your bookmarks/favorites and select the one that you just saved. It will then got through all of the links and verify them if they are good or bad. Good is marked in green and bad are marked in red! Give this code to your webmaster!
The test page for you.
There are good and bad links for you!
Now have you seen anyone else use AJAX like this? I do not think so. Hopefully you can see why AJAX is not hype. You can make it do things that you can run from a command in your bookmarks! Now below is the source code so you can save it to your server. Change the bookmark to point to where you saved this document.
//Set those global variables!
var reqXML;
var url;
var arrLinks;
var intErrors = 0;
var currentLink = 0; //We need a counter!
var timeOutTimer;
var maxWaitTime = 10000; //Milliseconds!
var strErrColor = "red";
var strValidColor = "green";
function TestThatLink(){
window.status = "testing: " + url.href;
timeOutTimer = setTimeout("reqXML='';intErrors++;FinishRequest('" + strErrColor + "');",maxWaitTime);
try {
if (netscape.security.PrivilegeManager.enablePrivilege) {
netscape.security.PrivilegeManager.enablePrivilege('UniversalBrowserRead');
}
}
catch (ex) { // eat it
}
if (window.XMLHttpRequest){
reqXML = new XMLHttpRequest();
reqXML.onreadystatechange = TestLink;
reqXML.open("GET", url.href, true);
reqXML.send(null);
}
else if(window.ActiveXObject){
reqXML = new ActiveXObject("Microsoft.XMLHTTP");
if(reqXML){
reqXML.onreadystatechange = TestLink;
reqXML.open("GET", url.href, true);
reqXML.send();
}
}
else{
alert("Test browser does not support this!");
}
}
function TestLink(){
try {
if (netscape.security.PrivilegeManager.enablePrivilege) {
netscape.security.PrivilegeManager.enablePrivilege('UniversalBrowserRead');
}
}
catch (ex) { // eat it
}
if(reqXML.readyState == 4){
window.clearTimeout(timeOutTimer);
try {
if(reqXML.status == 200){
strColor = strValidColor;
}
else{
strColor = strErrColor;
intErrors++;
}
}
catch(ex){
strColor = strErrColor;
intErrors++;
}
FinishRequest(strColor);
}
}
function FinishRequest(xColor){
window.clearTimeout(timeOutTimer);
url.style.backgroundColor = xColor;
currentLink++;
if(arrLinks.length > currentLink){
url = arrLinks[currentLink];
TestThatLink();
}
else{
alert(intErrors + " broken link(s) were found!");
window.status = "done";
}
}
arrLinks = document.links; //Grab those Links
url = arrLinks[currentLink]; //Get the link
TestThatLink()
Hopefully you can understand what is going on in the code. We are grabbing all of the links, checking to see if they exist, and showing the result on the page. See AJAX does not need to use server side code like everyone says! If you want to understand more about this code, ask away in the comments in this page. (If I do not answer, it is because I am sitting on the beach!)
Now it is Friday, so I think we need to put your brain to rest until Monday where we will talk about AJAX with server side code! But if you want to see a Moderator’s game that uses AJAX, take a look at Bear’s Blackbox here: Blackbox. Or you can sit back and play my JavaScript game (no AJAX) until my bandwidth is used up: Reversi.
Eric Pascarello
Moderator of HTML/JavaScript at www.JavaRanch.com
Author of: JavaScript: Your Visual Blueprint for Dynamic Web Pages
