How do i get the response back from server after issuing a request object(AJAX)
I was studying about AJAX and it was about form validation where as soon as the person fills in the username for signing up, it is checked using AJAX while he still can enter all the other fields. so i issued a request and on readystatechange i called a callback function. now i have studied PHP before this, but i never came across returning information from the server. I mean to say that w开发者_开发知识库hat all goes in my PHP script, and how does i make sure that the request issued is responded as desired. i dont want the exact code, if just bits of it,or the algorithm can be improved,
For example, i know i passed the username along with the url to the php script, and then i checked if it matched any of the existing usernames in my database(MYSQL and queries) , and normally i would just print the form again if there's a match, else i will exit(); but what do i do when i want to respond back to the object request?
It's really quite easy when you get the hang of it. It's even easier if you use jQuery's AJAX, http://api.jquery.com/jQuery.ajax/ - though don't bloat your site with this unless you intend on using loads of javascript (and use google's cdn for it)
In javascript, you make an XHR request either GET or POST to your PHP script. Usually you'll need to create a separate file for the view to any AJAX requests, because AJAX requests shouldn't bring the webpage's template back as well (i.e. if you wanted to return '1', it should only return '1', not <html><body>1</body></html>. ... etc.
Example:
blah.com/index.php needs some AJAX requests.
blah.com has javascript that creates the ajax request by sending a datastring/url (e.g. ajax.php?act=verify_email&email=a@c
blah.com/ajax.php would then have some PHP code that could switch($_GET['act'] or $_POST['act']) with a 'case' statement of 'verify_email'. That code would run some regex or something, and return 1 or 0 to say 1(valid), 0 (invalid). The 'onreadystatechange' holds the status of the request, so I think its usually a function i.e.:
xmlhttp.onreadystatechange=function()
{
if (xmlhttp.readyState==4 && xmlhttp.status==200)
{
document.getElementById("myDiv").innerHTML=xmlhttp.responseText;
}
}
You access the returned '0' or '1' through the xmlhttp.responseText, where xmlhttp is var xmlhttp =new XMLHttpRequest();
Then you just run the request
xmlhttp.open("GET","ajax.php?act=verify_email&email="+document.getElementById('email').value,true);
xmlhttp.send();
Update: In your case with the form, onblur (when they move out of focus of an element), you could run the AJAX request sending the value of the input, and then in the ajax.php script as a GET or POST request, you could run your validation query to check if the user exists already, or if the username isn't valid or whatever. Once the request has completed, it will return the results in the responseText value. Use firebug's console to check the result of an AJAX request if you can, its very useful.
This might not be what you mean but can't you:
xmlhttp.onreadystatechange = function() {
if (xmlhttp.readyState == 4 && xmlhttp.status == 200)
// do something with "xmlhttp.responseText"
var x = xmlhttp.responseText
}
And in the php just:
echo $x;
That works fine for transmitting strings and other info...
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