Simple client-side framework/pattern to simplify doing async calls?

Question

We're currently not using any serious client side framework besides jQuery (and jQuery.ui + validation + form wizard plugins).

A problem that surfaces a few times in our code is this:

1. We have a button that initiates an Ajax call to the server.
2. While the call is taking place, we display a "loading" icon with some text
3. If the server returns a result too quickly (e.g. < 200 ms), we "sleep" for 200 millis (using setTimeout()), to prevent flickering of the waiting icon & text.
4. After max(the call returns, a minimal timeout), we clear the loading icon & text.
5. We then either display an error text, if there was some problem in the ajax call (the server doesn't return 500, but a custom json that has an "error message" property. In fact, sometimes we have such a property in the response per form field ... and we then match errors to form fields ... but I digress).
6. In case of success, we do ... something (depends on the situation).

I'm trying to minimize code reuse, and either write or reuse a pattern / piece of code / framework that does this. While I probably won't start using an entire new heavy-duty framework just for this use case, I would still like to know what my options are ... perhaps such a client-side framework would be good for other things as well. If there's a lightweight framework that doesn't require me to turn all my code upside down, and I could use just on specific cases, then we might actually use it instead of reinventing the wheel.

I just recently heard about Ember.js - is it a good fit for solving this problem? How would you solve it?

Answer 1

$(function(){
 var buttonSelector = "#button";
 $('body').on({'click': function(evt){
    var $button = $(this);
    $button.toggleClass('loading');
    var time = new Date();
    $.get('some/ajax').then(function(data,text,jqXhr){
   // typical guess at load work
       $button.empty();
       $(data).wrap($button);
    }).fail(function(data,text,jqXhr){
     alert("failed");
    }).done(function(data,text,jqXhr){
       var elapsed = new Date();
      if((elapsed - time) < 200){
        alert("to short, wait");
      }
      $button.toggleClass('loading');
    });
  }},buttonSelector,null);
});

Answer 2

Just wrap the $.ajax in your own function. that way you can implement your own queing etc. I would suggest to do a jquery component for this. It can get pretty powerful, for example you can also pass http headers etc.
Regarding frameworks it depends on your requirements.
For example, you may consider Kendo UI, it has good framework for creating data sources: http://demos.kendoui.com/web/datasource/index.html.

Answer 3

Working Sample Code (well, almost)

I was going for something along the lines of @DefyGravity's answer anyway - his idea is good, but is still pseudo-code/not fully complete. Here is my working code (almost working demo, up to the Ajax URL itself, and UI tweaks)

The code & usage example:

jQuery.fn.disable = function() {
    $(this).attr("disabled", "disabled");
    $(this).removeClass("enabled");

    // Special handling of jquery-ui buttons: http://stackoverflow.com/questions/3646408/how-can-i-disable-a-button-on-a-jquery-ui-dialog
    $(this).filter("button").button({disabled: true});
};
jQuery.fn.enable = function() {
    $(this).removeAttr("disabled");
    $(this).addClass("enabled");
    // Special handling of jquery-ui buttons: http://stackoverflow.com/questions/3646408/how-can-i-disable-a-button-on-a-jquery-ui-dialog
    $(this).filter("button").button({disabled: false});
};


function AjaxCallbackWaiter(ajaxUrl, button, notificationArea, loadingMessage, errorMessage, inSuccessHandler, inFailureHandler) {
    // Every request that takes less than this, will be intentionally delayed to prevent a flickering effect
    // http://ripper234.com/p/sometimes-a-little-sleep-is-ok/
    var minimalRequestTime = 800;
    var loadingIconUrl = 'http://loadinfo.net/images/preview/11_cyrcle_one_24.gif?1200916238';

    var loadingImageContent = $("<img class='loading-image small' src='" + loadingIconUrl + "'/><span class='loading-text'>" + loadingMessage + "</span>");
    var errorContentTemplate = $("<span class='error ajax-errors'></span>");

    var requestSentTime = null;

    button.click(clickHandler);

    function displayLoadingMessage() {
        clearNotificationArea();
        notificationArea.html(loadingImageContent);
    }

    function clearNotificationArea() {
        notificationArea.html("");
    }

    function displayError(message) {
        var errorContent = errorContentTemplate.clone(errorContentTemplate).html(message);
        notificationArea.html(errorContent);
    }

    function ajaxHandler(result) {
        var requestReceivedTime = new Date().getTime();
        var timeElapsed = requestReceivedTime - requestSentTime;
        // Reset requestSentTime, preparing it for the next request
        requestSentTime = null;

        var sleepTime = Math.max(0, minimalRequestTime - timeElapsed);

        function action() {
            clearNotificationArea();
            button.enable();
            if (result) {
                inSuccessHandler();
            } else {
                displayError(errorMessage);
                inFailureHandler();
            }
        }

        if (sleepTime <= 0) {
            action();
        } else {
            setTimeout(action, sleepTime);
        }
    }

    function failureHandler() {

    }

    function clickHandler(){
        if (requestSentTime !== null) {
            logError("Bad state, expected null");
        }
        requestSentTime = new Date().getTime();
        displayLoadingMessage();
        button.disable();
        $.get(ajaxUrl, 'json').then(ajaxHandler, failureHandler);
    }
}

// Usage:
var ajaxUrl = 'FILL IN YOUR OWN URL HERE';
var button = $("#clickme");
var notificationArea = $(".ajax-notification-area");

var waitingMessage = "Doing Stuff";
var errorMessage = "Not Good<br/> Please try again";

$(document).ready(function(){
  new AjaxCallbackWaiter(
    ajaxUrl,
    button, 
    notificationArea,
    waitingMessage,
    errorMessage,
    function(){
      alert("All is well with the world");
    },
    function(){
      alert("Not good - winter is coming");
    });
});