Tips for loading jQuery in mobile apps

Whether you are using jQuery by itself or with Bootstrap there are a few things to remember if you don’t want to see the following error: “Uncaught ReferenceError: $ is not defined”.  This error happens because you are trying to access jQuery before the library has finished loading. There are several ways to fix the error.

Encapsulate jQuery functionality inside a function. This keeps the parser from attempting to execute any jQuery until the function is explicitly called and it allows us to place the script tag at the bottom of the app. This approach can get tricky if jQuery is slow to load. It’s possible that the button can be visible and clickable before jQuery has finished loading. If this happens your app will throw an error. You can try it out in jsfiddle here.


<!DOCTYPE html>
<head lang="en">
    <title>jQuery Test</title>
</head>
<body>

<button id="button1">Click me</button>
<div id="div1" style="background:blue;height:100px;width:100px;position:absolute;"></div>
<script>

    // Test if jQuery is available
    if(typeof jQuery !== 'undefined'){
        console.log("jQuery has been loaded");
    }
    else{
        console.log("jQuery has not been loaded");
    }

    document.getElementById("button1").onclick = function(){
        $( "#div1" ).animate({
            left: "250px",
            height:'150px',
            width:'150px'
        });
    };

</script>
<!-- Everything above this will load first! -->
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js" ></script>
</body>
</html>

Use the script tag onload event to initialize jQuery functionality. This follows the guidelines of the first suggestion above and then waits to fire off any functionality until after the jQuery library has completed loading. This insures jQuery is loaded before it can be used. You can try it out in jsfiddle here.

<!DOCTYPE html>
<head lang="en">
    <title>jQuery Test</title>
</head>
<body>
<div id="div1" style="background:blue;height:100px;width:100px;position:absolute;"></div>
<script>

    // Test if jQuery is available
    if(typeof jQuery !== 'undefined'){
        console.log("jQuery has been loaded");
    }
    else{
        console.log("jQuery has not been loaded");
    }

    // Run this function as soon as jQuery loads
    function ready(){
        $( "#div1" ).animate({
            left: "250px",
            height:'150px',
            width:'150px'
        });
    }

</script>
<!-- Everything above this will load first! -->
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js" onload="ready()" ></script>
</body>
</html>

Place script tag in head. Sometimes lifecycle issues in mobile web apps will require us to simply load jQuery from the head of the web app. Because this forces jQuery to load synchronously before any user interface elements we pretty much guarantee that jQuery will be available when we run JavaScript within the body of the application. Try it out in jsfiddle here.


<!DOCTYPE html>
<html>
<head lang="en">
    <meta charset="UTF-8">
    <title>jQuery Test</title>
    <!-- Block DOM loading until jQuery is loaded -->
    <script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>
</head>
<body>
    <button id="button1">Click me</button>
    <script>

        // Test if jQuery is available
        if(typeof jQuery !== 'undefined'){
            console.log("jQuery has been loaded");
        }
        else{
            console.log("jQuery has not been loaded");
        }

        // Page is fully loaded including any graphics
        $(window).load(function() {
            console.log("window.load worked!");
        });

        // According to jQuery docs this is equivalent
        // to the generic anonymous function below
        $(document).ready(function() {
            console.log("document.ready worked!");
        });

        // The DOM has been loaded and can be accessed
        $(function() {
            console.log("DOM loaded worked!");
        });

        $( "#button1" ).click(function() {
            alert( "Handler for .click() called." );
        });

    </script>
</body>
</html>

What all mobile web devs should know about PhoneGap

If you already building or looking into getting started with mobile web applications you should understand the basics of PhoneGap. The name ‘PhoneGap’ is widely recognized, and perhaps more widely misunderstood.

The nudge to write this article was born out of conversations where we stumbled across concrete limitations to modern responsive JavaScript libraries such as bootstrap and jQuery. Limitations that cannot be overcome by adding more brilliant functionality because some JavaScript capabilities simply do not exist within the browser today. Furthermore, other requirements were imposed by political realities, timeframes and expectations.

That’s where PhoneGap steps in. 

So what, tell me what PhoneGap does?

PhoneGap is owned by Adobe and it has an open source top-level Apache Foundation sister project called Cordova. I won’t bore you with its long and twisted history, you can read about it here if you want.

The bottom line is PhoneGap allows you to develop JavaScript mobile applications that have access to certain aspects of the native device such as writing data to a filesystem. Your web application is wrapped within a native mobile application container that gives you JavaScript access to native operating system capabilities beyond what the browser itself is capable of doing!

By native I mean iOS Objective C, Android Java, WindowsPhone, Windows 8, Blackberry 10, Amazon Fire OS and Tizen. Your JavaScript applications runs in a chrome-less browser that gives you special hooks to the operating system. You can also submit PhoneGap applications to the AppStore, Google Play and others.

Who uses this stuff, well you may be using a PhoneGap app from one of these online stores and not even know it. To mention a few: Southwest Airlines and many others.

What limitations can PhoneGap address that responsive libraries don’t?

If your requirements call for all or most of the following items, then PhoneGap is the correct choice for your project today. That may change as HTML5 continues to rapidly grow, but for now I’m sticking with the following bullet points. Stick with me and read through all of these before starting to throw out counter arguments.

JavaScript skillz. If you are an existing JavaScript shop, then PhoneGap leverages your existing JavaScript skills to access capabilities beyond current browser functionality without the need to have an in-depth understanding of Objective C or Java.

Sure, it’s easy to say you can hire expert contractors to develop iOS and Android applications, along with UX designers and testers. But, if your budget doesn’t include the capital costs for these folks and all you have is JavaScript ninjas on staff then the choice is easy.

Or, maybe you have genius-level developers that could easily and quickly spin up on all your need to know on ObjectiveC and Java Android. If this isn’t the case, and your timeframes and budgets don’t allow for this then you’ll need a fallback plan such as PhoneGap.

Access to camera.  Yes, you can currently access the camera on some web browsers today. However, the support on mobile browsers is still inconsistent, limited or non-existent. On the other hand, native device OS’s are expected to have access to cameras If they didn’t it would be considered a serious oversight. PhoneGap provides cross-platform mobile device access to the camera.

Read/write access to SD Card. Just to reiterate, this is both read and write access to a local storage device. Certainly there is a FileReader API in plain old JavaScript, but as far as I know there isn’t a FileWriter or its equivalent yet. If you need the write access to go along with read capabilities then you should be looking at PhoneGap.

[Correction Jan. 27, 2014] I mis-wrote. The FileWriter API exists however it has limited supported across browsers: http://caniuse.com/#search=filewriter. And, examples of it’s use can be found here.

AppStore or Google Play. If you have a requirement to submit your application to the app store then PhoneGap will help you get there. There is no way today for submitting a stand-alone web application for acceptance on AppStore or Google Play. Period. Some will argue that the need for using these online application stores is going away, but that’s a non-issue if you have been directed to meet this requirement a.s.a.p. and your job depends on it. If that’s the case, then PhoneGap will be your friend.

Is there anything else I should know?

Yes…First, PhoneGap is not perfect, but then again few software projects are perfect. You will need to install and know a few things about the native IDEs you want to support. If you want to deploy Android you’ll need to install Eclipse or IntelliJ. For iOS you’ll need to install XCode. Etc. You still have to compile a native project or you can try your hand at Adobe’s PhoneGap Build, which is a cloud based build system for PhoneGap.

It is confusing that there are two projects that share a common/similar code base: PhoneGap and Cordova. Also, Cordova’s documentation has typically been more up to date that Adobe’s. If you do your research you’ll find various performance complaints and bug issues (like I just said are there any software projects that don’t have these??).  Yet, overall it’s a great starting point if you have the needs listed above, and it’s much better than trying to start from scratch given today’s dramatically shortened delivery expectations.

You can absolutely still use bootstrap, jQuery and other JavaScript libraries within PhoneGap. There are caveats, of course, related to application life-cycle issue, navigation as well as App Store and Google Play user interface acceptance guidelines.

If you want to add functionality to PhoneGap because you find some critical thing is missing that you need for your project, the good news is you can develop a custom plug-in.

Last, I should mention Titanium Studio. It also lets you leverage JavaScript skills, with the primary difference being that it converts JavaScript into native byte code rather than just displaying it in a chrome-less view.  Plus it’s comes with its own IDE and MVC Framework.  I’ve never used Titanium so I can’t judge it, however I know people who do use it successfully and love it. It’s one more thing to consider that you should be aware of.

References

Cordova Documentation

PhoneGap Documentation

PhoneGap Platform Support

Two languages that software developers should be familiar with

The question that I get asked the most these days is “what development languages should I be learning [to stay competitive/excited/motivated/etc] ?” The high-tech industry, and software in particular, is changing at a ridiculously fast pace and that introduces a lot of uncertainty and confusion as well as great opportunity. My answer to this question is unequivocal: I think for the foreseeable future developers should be learning the basic concepts of JavaScript and Python. If you don’t already have these skills then you simply cannot go wrong with this approach. If you’ve been a long-time server-side developer, or you are just getting started with software development then knowing the patterns and practices for JavaScript and Python will serve you well.

Why?

There are three primary reasons and I’ll try to be short and to the point. First, there are at least 2.5 billion internet users world wide, and that number is growing. Their primary method of accessing the web is a browser and JavaScript is the lingua franca of the browser world. JavaScript is a scripting language and it is “the” fundamental building block that allows web pages to “do” things such as submitting your search request to a server, or helping to find your location from your phone. Almost all web pages being served up around the world have JavaScript in them.

Second, the majority of retail, commercial and governmental web applications have a requirement that calls for the use of “server-side” code. This is code, such as Python, that runs on a server and not in the browser application. The most common functionality of server-side code is passing data back and forth between a database and a web application. For example, if a web app asks for a username and password, that user name and password are almost always stored on a server somewhere and not, for security reasons, in the web page and on the client browser where it could be very easily stolen.

Third, you can absolutely apply these client-server patterns and practices to other languages used within the realm of web development. A User Interface designer who has been solely focused on layout and styling via Cascading Style Sheets (CSS) can now understand and appreciate how the underlying JavaScript code can affect the look, feel and behavior of a web page. Python skills can also be used a springboard for more quickly learning other powerful web development platforms such as ruby-on-rails.

The bottom line is if you understand both client development (JavaScript) and server development (Python), then you start to gain considerable value as someone who understands how to help the entire system work together in harmony.

A short note on jQuery.

Many (most?) new web developers learn jQuery first. However, even if you know jQuery you don’t necessarily understand JavaScript. The awesome jQuery libraries provide an interface that hides and simplifies a lot of native JavaScript hoopla, and in general can really make life significantly easier and save time when building modern cross-browser web apps. jQuery is built using JavaScript (and CSS3), but it is not JavaScript. Because of that, when something goes wrong or not as you expected (not if, but when!), and you have a general understanding of how JavaScript works, then you stand a much better chance of figuring out a timely work-around with significantly less stress, frustration and time wasted towards your projects deadline.

The absolute minimum recommended reading list:

JavaScript.

  • Douglas Crockford’s book “JavaScript: the good parts”.
  • Douglas Crockford’s website – He is considered a key brainchild behind the ongoing development and understanding of JavaScript.
  • W3schools – An excellent website for anyone using or learning JavaScript. It has tutorials and online Try It Yourself sample apps.

Python.

jQuery Mobile – Setting full content width

Here are some hints to help get all of your jQuery content stretched to the full width of your mobile browser screen regardless of screen size or orientation. These techniques have been tested on jQuery 1.7.x, jQuery 2.0 and jQuery mobile 1.3.1.

Lets start with a look at the minimum required CSS:

html,body,div[data-role ="page"], div[data-role="content"] {
    height: 100%;
    width: 100%;
    margin: 0px;
    padding: 0px;
}

Problem – Using the minimum CSS above, leaves a spacer on the top and left hand sides of the app, and the right hand border and/or bottom border disappears. I noticed the right hand margin extends approximately 9 to 15 pixels (or greater depending on device) beyond the visible view. I verified this behavior on Android 4.1 native browser and Chrome 26, as well as on iPad 3 using Safari and Chrome 25.

Solution – set certain CSS width properties as shown below. This solution has been tested on Android 4.1 native and Chome 26, Android 2.3.2 native, and on iPad Safari and Chrome 25. Just a bit of a warning that if displayed on a desktop browser you will see vertical scrollbars. But, you should be detecting the different between mobile and desktop anyway, right!

Note: this solution doesn’t address the problem with content height, it only looks at width. So, yes, you will notice that the height of my sample is off the page.


<!DOCTYPE html>
<html>
<head>
    <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
    <meta http-equiv="X-UA-Compatible" content="IE=7,IE=9">
    <meta name="apple-mobile-web-app-capable" content="yes">
    <meta name="viewport" content="width=device-width, initial-scale=1.0, maximum-scale=1.0,user-scalable=no">
    <meta name="apple-mobile-web-app-status-bar-style" content="black-translucent">

    <title>jQuery Test</title>

    <link rel="stylesheet" href="http://code.jquery.com/mobile/1.3.0/jquery.mobile-1.3.0.min.css" />

    <script type="text/javascript" src="http://code.jquery.com/jquery-2.0.0.js"></script>
    <script type="text/javascript" src="http://code.jquery.com/mobile/1.3.1/jquery.mobile-1.3.1.js"></script>
<style>
        html,body, div[data-role ="page"] {
            height: 100%;
            width: 100%;
            margin: 0px;
            padding: 0px;
        }

         .ui-content{
            height: 100%;
            width: 100%;
            margin: 0px;
            padding: 0px;
            border-style: solid;
            border-color: chartreuse;
            border-width: 5px;
        }

        #map {
            height: 100%;
            width: 100%;
            padding: 0px;
            border-style: solid;
            border-color: crimson;
            border-width: 10px;
        }
</style>
</head>

<body>

<div data-role="page" id="page1" >

    <div data-role="content">
        <div id="map"</div>
    </div>

</div>
</body>

References

Determining the dimensions of an [HTML] element

Check HTML5 Browser Height and Width using Canvas

[Modified April 26, 2013 – fixed code bug]

The problem with JavaScript Obfuscators and Minification – Tracking down errors

JavaScript obfuscators and minifiers do their job well. In fact, some obfuscators have anti-debugging features. However, if you are a legitimate developer building applications against one of these libraries, chances are you’ve gotten an indecipherable error such as “z=null line 14300” and it brings your development efforts to a halt. Error messages like this provide no useful information on what the problem really is, or give any hints on how you might be able solve it. You’ve probably even looked at the jumbled source code in a last ditch attempt to make some sense out of the error. And, whether it’s your own library or a mainstream ones as jQuery or Dojo, it doesn’t matter. The amount of productivity lost because of these errors in probably very large, not to mention the frustration it causes.

I hope the the developers of these obfuscators are reading this…because I have a proposed solution to the problem.

Now, I want to start out by mentioning that I fully understand why obfuscators exist for reasons such as source code protection and decreasing download size. What I propose takes this fully into account, yet makes your library developer friendly in a secure way:

During the obfuscation process create an index file that maps each variable, function and class to a real line number and store this file in a web folder.  Then create a small html file that lets you search the index and return the real line number. Provide an option for return the variable, function or class name, too.

The concept is that if there is an error, like the  “z=null line 14300” I mentioned above, developers can then at least have some hope of narrowing down the general area of the code where it might be occurring.

The bonus is, if you own an obfuscated commercial library, now your tech support people can also look up the general area where a customer might be having a problem. For security reasons you don’t have to share the index file, But, even then, there isn’t enough information in it to de-compile the library. Now, if I post my error to the forum:  What is “z=null line 14300”? Tech support will be able to tell me that I’m missing a custom property on a widget’s HTML DIV element. It’s a win-win situation.

What do you think?

Simple Native JavaScript Classes – So simple a caveman could do it.

Among the many things I severely dislike about JavaScript is working with applications that have oodles of global variables, multiple .js libraries and dozens of loosely organized, individual functions. This is a very common pattern (or perhaps an anti-pattern). But it’s a terrible way to code for medium to large projects, especially where you have to share your code. Here’s a highly simplified example:


var someNumber = 2; //Global variable

function add(number){
    return someNumber + number;
};
alert(add(4)); //displays "6"

It’s unfortunate that this pattern is reinforced in authoritative books, blogs and articles. It’s completely pervasive in the majority of examples you see on the web. The downside is modifying, testing and troubleshooting this pattern can be an absolute nightmare. I compare it to building a fragile, multi-level house of cards: one wrong bump and it all falls down.

There is a better way!

So, I offer an easy-to-implement solution: where possible place your functions and properties in Class-like objects and all will be so much better. It’s not quite what you get with strongly-typed object oriented languages like C# or Java, but it works. Besides, if you use this pattern in your project then cats and dogs will live peacefully side-by-side and the universe will be in balance. The best news: this works perfectly fine with plain old JavaScript (POJO). And, if you are using something like jQuery use can use some version of Classes with those too, and I highly recommend it.

Here’s the fundamental pattern of a JavaScript Class:

function Add(){};
var someMath = new Add();

That’s very easy…right?? The advantages are many and include the following:

  • You get a powerful framework for logically grouping functionality. This lends to scalability and ultimately stability in your projects.
  • You can easily extend this pattern using prototypal inheritance.
  • You can take advantage of encapsulation.
  • You can implement inheritance and polymorphism.
Now let’s put this pattern to use. I’m providing two examples here. There are several other syntactical ways of doing this, but for brevity I’m sticking with two. The first example uses a very basic Object to implement namespace-like behavior. I say namespace-like because it’s not a true namespace like in C# or Java. The second example uses the built-in windows Object as a way of passing the namespace information. Click here to download a sample app that demonstrates these concepts.

POJO Class Pattern using Object Namespaces

Here’s an expanded example of the pattern with two levels of namespace separation using a standard Object :

if (!com) var com = {};    //1st level namespace
if (!com.ag) com.ag = {};  //2nd level namespace
if (!com.ag.Add) {
    com.ag.Add = function (value) {
        /// <summary>Demonstrates the plain old JavaScript pattern for classes.</summary>
        /// <param name="value" type="Number">Any number.</param>

        this.getValue = function () {
            /// <summary>Returns the property passed to the constructor.</summary>
            /// <returns type="Number">A number that was passed to the constructor.</returns>
            return value;
        },

        this.add = function (number) {
            /// <summary>This method adds value property + number</summary>
            /// <param name="number" type="Number">The number we want to add.</param>
            /// <returns type="Number">The number passed to the contructor plus this number</returns>
            return value + number;
        }

        //For Visual Studio intellisense cues
        com.__namespace = true;
        com.ag.__namespace = true;
        com.ag.Add.__class = true;
    }
}

And, here’s how to use this class:

var test = new com.ag.Add(2);
alert(test.add(4)); //displays "6"

POJO  Class Pattern using window[] Namespaces

Here is a slightly different version of the pattern that uses the window object, the results are the same:

if (!window["NS"]) window["NS"] = {};

window["NS"].Add = function (value) {
    /// <summary>This class uses addition</summary>
    /// <param name="value" type="Number">The number we pass to the contructor.</param>

    this.getValue = function () {
        /// <summary>Returns the private property called value.</summary>
        /// <returns type="Number">The number passed to the contructor.</returns>
        return value;
    },

            this.add = function (number) {
                /// <summary>This method adds value + number</summary>
                /// <param name="number" type="Number">The value we want to add.</param>
                /// <returns type="Number">The number passed to the contructor plus this number</returns>
                return value + number;
            }

    //For Visual Studio intellisense cues
    window["NS"].__namespace = true;
    window["NS"].Add.__class = true;
}

Here’s an example of how to use this class:

var test = new NS.Add(2);
alert(test.add(4)); //displays "6"

You are probably wondering about the funky xml comments. That’s for Visual Studio 2010’s built-in intellisense. I think but I’m not 100% certain that these work with Visual Studio Express as well. If you know for sure then please drop a comment. Notepad++ and other tools are okay for small projects but you can thank me later when you use this Class pattern along with built-in intellisense for any project that involves more than a dozen or so functions. And that’s not all – you can also see intellisense across different .js libraries. It’s all about productivity and ease-of-debugging. And, everyone will thank you when they have to re-use your code.

I’ve also attached a screenshot below to show you what the Visual Studio intellisense looks like. Also note in this example, the physical file, Add.js, in in the directory /scripts/com/ag/Add.js and I’m writing code in index.html which is at the root directory. How cool is that?!

 References

Sample application that demonstrates the Class concepts

Douglas Crockford’s [awesome] JavaScript Blog

Visual Studio JavaScript Intellisense Revisited

Creating Advanced [JavaScript] Web Applications with Object Oriented Techniques

Object Oriented Programming in JavaScript

Write Object Oriented JavaScript Part 1

The Format for JavaScript Doc Comments (Visual Studio)