Example: jQuery AJAX POST with PHP

Basic usage of .ajax would look something like this:

HTML:

<form id="foo">

    <label for="bar">A bar</label>
    <input id="bar" name="bar" type="text" value="" />

    <input type="submit" value="Send" />

</form>

JavaScript:

// variable to hold request
var request;
// bind to the submit event of our form
$("#foo").submit(function(event){
    // abort any pending request
    if (request) {
        request.abort();
    }
    // setup some local variables
    var $form = $(this);
    // let's select and cache all the fields
    var $inputs = $form.find("input, select, button, textarea");
    // serialize the data in the form
    var serializedData = $form.serialize();

    // let's disable the inputs for the duration of the ajax request
    // Note: we disable elements AFTER the form data has been serialized.
    // Disabled form elements will not be serialized.
    $inputs.prop("disabled", true);

    // fire off the request to /form.php
    request = $.ajax({
        url: "/form.php",
        type: "post",
        data: serializedData
    });

    // callback handler that will be called on success
    request.done(function (response, textStatus, jqXHR){
        // log a message to the console
        console.log("Hooray, it worked!");
    });

    // callback handler that will be called on failure
    request.fail(function (jqXHR, textStatus, errorThrown){
        // log the error to the console
        console.error(
            "The following error occured: "+
            textStatus, errorThrown
        );
    });

    // callback handler that will be called regardless
    // if the request failed or succeeded
    request.always(function () {
        // reenable the inputs
        $inputs.prop("disabled", false);
    });

    // prevent default posting of form
    event.preventDefault();
});

Note: Since jQuery 1.8, .success, .error and .complete are deprecated in favor of .done, .fail and .always.

Note: Remember that the above snippet has to be done after DOM ready, so you should put it inside a $(document).ready() handler (or use the $() shorthand).

Tip: You can chain the callback handlers like this: $.ajax().done().fail().always();

PHP (i.e. form.php):

// you can access the values posted by jQuery.ajax
// through the global variable $_POST, like this:
$bar = $_POST['bar'];

Note: Always sanitize posted data, to prevent injections and other malicious code.

You could also use the shorthand .post in place of .ajax in the above JavaScript code:

$.post('/form.php', serializedData, function(response) {
    // log the response to the console
    console.log("Response: "+response);
});

Note: The above JavaScript is made to work with jQuery 1.8 but should work with previous versions down to jQuery 1.5.