Tag Archives: JavaScript

AngularJS Services and Promises

Promises, Deferred, Futures

Call it what you will, promises are another mechanism for dealing with the asynchronous nature of some things you’ll do within JavaScript. For example, calling remote services, timers, animations completing, etc. In each case you could just have a callback, but what if you wanted to attach several callbacks to the completion or failure of a single asynchronous job? That’s difficult with callbacks, but promises make it easy.

Promises make it easy to tie together several asynchronous actions and treat them as one. This makes it easy to react only when all have completed or one of them had a problem. This is a much better solution than the nesting of callbacks you often see done in JavaScript code. Nested callbacks are often written in a way that forces requests to be made serially when they could be executed in parallel and perform better as a result.

Promises can simplify code in another way because a promise which has already resolved and one which has yet to resolve are treated are both used in exactly the same way.

Promises in AngularJS

AngularJS offers promises via a service called $q. It is modeled after a promise library called (not surprisingly) Q. You’ll see promises returned from several of AngularJS’s services, including $http (for service calls), $timeout, and $route (though I admit I’m not sure how it’s being used in the latter case).

AngularJS even has support for promises being assigned directly to $scope variables. So you can take the promise you get back from a remote service call and assign it directly to a variable knowing that when the service call finally returns, the variable will be updated and any binding attached to the variable will redisplay. That’s significantly easier than other frameworks I’ve used in the past.

Service Calls

I thought I’d give three examples of calling a service with $http and show how the promise it returns may be used directly, and examples of how caching and aggregation can be made easier thanks to promises.

For these examples I’m just calling the OpenKeyval service to store and retrieve some JSON data. It’s simple, it’s free, and I know I can count on any code I give you being able to access it without any special API key.

Source code for all of the following and more is here: https://github.com/JohnMunsch/AngularJSExamples, in particular look at the app/scripts/controllers/promises.js and app/view/promises.html to see the code specific to these examples.

Click here to see all of the following as running examples on Github

    • Example 1: Store and retrieve some values. Promises returned from $http are assigned directly to $scope variables and AngularJS dereferences them automatically.
    • Example 2: Make multiple calls to different services aggregating the results of all the calls and merging the results into a single returned value.
    • Example 3: A common pattern for services is to be able to satisfy requests from a local cache when appropriate. Promises can make that an easy upgrade for an existing service.

A Shortcoming

$q is not as full featured as Q is. That’s not surprising because AngularJS is only trying to provide as much functionality as it needs without requiring you to load up another library. AngularJS does the same kind of thing when it comes to jQuery. It has a minimal subset of functionality built in (called jQLite) that it uses if jQuery wasn’t loaded prior to loading AngularJS.

However, this is where things suddenly differ. If you do load jQuery prior to loading AngularJS then it won’t use it’s own built in version, but will instead use the more full-featured jQuery implementation. However, as far as I know, loading up the Q library or jQuery before you load up AngularJS doesn’t cause AngularJS to use Q promises or jQuery Deferred objects instead of its own subset implementation. That seems to me like an oversight or shortcoming to their implementation.

Nevertheless, I hope I’ve shown with the examples above that you can still do some really interesting things even with the limited set of functionality $q provides.

Follow Up

After a few weeks I realized that something I didn’t really cover is how assigning a promise to a variable in $scope can hinder access of that same variable in the controller. For example, if you do something like this:

$scope.someValue = $http.get(someURL);

You’ve assigned a promise to the variable and from the standpoint of code in your view, nothing really changed. You can still do {{someValue.someSubValue}} and act blissfully unaware that someValue is a promise rather than a JavaScript object. But, try the same thing from the controller code and you’ll have all kinds of problems. $scope.someValue.someSubValue isn’t anything you can access in the controller because $scope.someValue is actually a promise and will always stay a promise, even once it’s resolved. The only thing that changes once it’s resolved is that any .then() function you call on it will immediately call the closure you pass into it with the value the promise now caches. Thus you will forever more have to use it within the controller like so:

$scope.someValue.then(function (value) { $log.info(value.someSubValue); });

If you have some values you’re getting via AJAX calls or via some other mechanism that returns a promise and you need to access them as much or more from a controller as from view code then only assign the resolved value into the scope and not the promise. For example:

$http.get(someURL).then(function (value) { $scope.someValue = value; });

In that case you’re waiting until the promise resolves and only assigning the final returned value into the scope. Now both the view code and the controller can directly access $scope.someValue.someSubValue freely.


Yeoman, Grunt, and Bower

Aside from being a top end legal team, Yeoman, Grunt, and Bower are also the names of some front-end development tools I use when working on new projects these days or whenever it’s going to be easier to throw together some code and test it out in a testbed rather than embedded in a larger project. First I’ll go over what role each of these has in the development of a modern website front-end. Then I’ll take a brief side trip into a tool (Node.js) which isn’t directly relevant to any of them, but one which is required in order to install them. Then we’ll get into some specifics for all three as I demonstrate using them to get started on an AngularJS project.

Yeoman is the code generator, it fulfills a role similar to that filled by the Rails app if you’ve ever used Ruby on Rails because it can be used to generate whole projects or individual pieces of code depending upon the specific code generators it has installed. It gives you a quick shell from which to start a project.

Grunt is the builder and utility tool. As with Yeoman it’s modular in nature and as a result it can fulfill a huge variety of roles. Typical things you might call upon Grunt to perform would be concatenating multiple CSS or JavaScript files together for faster download, minifying CSS or JavaScript files (again for faster download), running a small local server to make developing your website easier, looking for errors in your JavaScript, running JavaScript unit tests, running compilation tools for CoffeeScript, LESS, or Sass, and the list goes on and on. If you have a Java background you might think of Ant as the closest analogy for Grunt.

Finally, Bower is your web component installer. If you find yourself needing to install a JavaScript library or a CSS/JavaScript framework, Bower can handle that and even make sure that any other components upon which it depends (for example, Backbone.js requires Underscore.js) are also automatically installed. Java tools like Maven and Ivy offer similar functionality so that each developer can get the libraries he/she needs installed without having to check all of them into version control systems with the code being developed.

That side trip I mentioned

As strange as it might seem to require an installation utility (npm) in order to install an installation utility (Bower), that’s exactly what I’m going to tell you to do. These days any JavaScript software worth its salt seems to be installed in much the same way. First you go get the latest version of Node.js (there’s a big green install button on the middle of the http://nodejs.org/ page). When you install that you’ll also pick up a nifty little utility known as the Node Package Manager or npm for short. With npm installed you can then install all three of the aforementioned tools Yeoman, Grunt, and Bower.

As I mentioned earlier, you use the npm tool you just installed to install the other three by running “npm install -g yo” (the details are covered on Yeoman’s website: http://yeoman.io/ but that’s actually all you have to do). You’ll see npm download, compile, and install tons of stuff but you won’t actually be involved in the process. In that respect it’s much like other package managers like Yum or RPM.

Finally you’ll need some kind of Yeoman generator installed in order in order to generate our starting shell: “npm install -g generator-angular”


With all the installation out of the way, let’s create a directory for a new project (“mkdir TestApp”), change directory into the newly created directory, and just type “yo” at the command line and see what we see.

YeomanPick “Run the Angular generator” and hit enter, then answer the various yes or no questions it asks in order to generate the shell you want for your app. At the end it will also run npm to install the local copies of tools you may need and Bower to install the various libraries you need for your shell (for example, AngularJS and jQuery).

Yeoman has now fulfilled most of its mission but I want to look at some files it generated and then come back to using it as a tool even after we have our shell. There are many files worth noting which Yeoman generated but three in particular are:

  • package.json – This file tells npm which Node.js packages need to be installed in this particular project. Most of what you’ll find in here are packages Grunt needs to do its job. Rather than installing these globally, they are instead installed on a project by project basis so you can have different versions of the tools used by different projects.
  • bower.json – This file tells Bower which components to install in the app/bower_components directory. These are JavaScript and CSS components which you’ll use within the website you’re building.
  • Gruntfile.js – This file is task instructions for Grunt so it knows how to perform a set of different tasks for a given project. If you look near the bottom of the file you’ll see that the Angular generator has created a file with the tasks “server”, “test”, and “build” which in turn call many other sub-tasks to perform their work.

Finally it’s worth noting that that’s not the final use that Yeoman can have in our development. Just as a Rails user can continue to use the Rails command to generate new models, migrations, etc. within an already constructed project, the Angular generator can be used to generate services, routes, directives, filters, etc. as detailed here: https://github.com/yeoman/generator-angular


Running Grunt from the command line with “grunt” should perform a default sequence where the JavaScript code is checked for errors, unit tests are run, and finally a “distribution” version of the application is built into the “dist” directory. Grunt will have concatenated CSS files and JavaScript files into common chunks like 7d151330.main.css, bd6ce9e3.plugins.js, c2ac0a01.scripts.js and the references to the original names within the HTML will have been replaced with the new file names. When you update some of your scripts and recompile, the file names will be different and there will be no need to worry about browsers continuing to use old cached versions of your scripts. You never have to perform this task, all of the files within the app directory may be deployed as soon as you are ready to do so, but Grunt performs a variety of optimization tasks which can make for a more performant site if you like.

One of the handiest things Grunt offers via the Gruntfile.js which was created is “grunt server”. Running that will compile files which you might have that need compiling (for example, if you use CoffeeScript rather than JavaScript or you’re using Sass), start up a server running the application, launch the index.html page in your default browser, and then watch for any changes to the files as you edit the CSS, HTML, and JavaScript and re-run compiles as needed and reload the page within the browser as you work on the website. I just love this feature because of how easy it makes it for me to work on features and immediately see the results in my browser, often I don’t even have to lift my fingers from the keyboard or switch apps to my browser because I can see if my changes accomplished what I want simply by looking at the automatically refreshed page.

At this point you would be forgiven for thinking that there was little point in installing Node.js except that it gave us the npm tool we needed to install all our other software, but actually Node.js is also being used behind the scenes by Grunt to run the local server I mentioned above.


Last but not least is Bower. It offers the opportunity to search for packages you may need in your project (for example, “bower search underscore” to find Underscore.js) and install them in your project (for example, “bower install –save underscore” to install the aforementioned package and add it to the list of dependencies in the bower.json file). Bower is also capable of understanding the difference between packages needed for development (for example, unit testing tools) and those needed for both development and runtime.

Since the .gitignore for the project will normally list both the app/bower_components and the node_packages directory, you won’t be checking in those pieces with your code (assuming you use Git as a version control mechanism). Instead, whenever checking out the project onto a new machine, just run “npm install” and “bower install” within the project directory and the tools will use the package.json and bower.json files to make sure all the needed pieces are installed.

But that’s not all

Keeping these tools up-to-date might prove difficult if not for the fact that the Node Package Manager is capable of doing so automatically via “npm update -g” for all your global software like Yeoman, Bower, etc. or “npm update” within the project directory to update Grunt packages, etc. I’m not going to contend that it always goes flawlessly, lots of this software is still beta and undergoing lots of changes so there have been days when I needed to remove it all and reinstall; but that’s rare and usually takes only a few minutes.

Changeable vector graphics with SVG and AngularJS

I’ve long been a fan of using SVG (Scalable Vector Graphics) to do images that I can change easily on the fly. When I say “long been a fan” I mean that when I first started doing it I hand wrote some SVG as XML to show a donation bar we needed for GameDev.net and I had a program that would change the amount thus far donated on the bar and run it through an early version of the Java Batik library to spit out a JPEG file we could put on the website. It was crude, but it sure beat making a new graphic two or three times a day.

Years later things have gotten a lot easier. Modern browsers have advanced to the point where you can include an SVG image in the page as easily as referring to them in an img tag like so, <img src=”something.svg”/>, or just dumping some SVG code straight into the middle of the HTML for your page like this <svg>…lots of vector graphics…</svg>. And editing? Why would you edit by hand anymore when Adobe Illustrator can generate SVG files of your drawings for you, or if you have no budget for such nice tools, Inkscape does a pretty good job and costs nothing.

So it occurred to me the other day that it would be interesting to see if I could use AngularJS and its ability to rewrite HTML on the fly and combine that with SVG in the browser to rewrite SVG on the fly. The answer is, it not only works, it’s downright easy to do so. I’ve provided a couple of different examples to show just how easy it is to so.

Example 1: Have a SVG graphic where I change text within the graphic automatically because it’s tied to a value in an AngularJS model.

Getting an image to start with was pretty easy. I went to The Noun Project and grabbed an icon of the sun I liked. It was provided by an unknown author in this case. The icon came in SVG format so all I did with it in Inkscape was add a little color and some text that showed the temperature. Then I saved that as a “Plain SVG” file rather than an “Inkscape SVG” file. It might have worked as well with the latter but I didn’t want any surprises.

Inkscape editing SVG icon

I then popped over to an HTML file I had generated and imported it with an image link like this:

<img alt="" src="images/sunshine_plus_temp.svg" />

I then hand edited the SVG file and found where the text for the temperature and replaced it with an AngularJS model variable reference. So:

<tspan sodipodi:role="line" id="tspan4542" x="97.124313" y="52.063747">87°</tspan>


<tspan sodipodi:role="line" id="tspan4542" x="97.124313" y="52.063747">{{temp}}°</tspan>

The <img> way of loading the SVG had to change because AngularJS wasn’t going to replace a variable inside an image for me. So I simply pasted the contents of the sunshine_plus_temp.svg right into the middle of a page already setup for AngularJS and put the temp variable into my $scope. It worked like a charm. With an input field tied to the model variable, as I typed, the SVG graphic was automatically updated with the new value.

My final touch was to externalize the SVG file. Nobody wants to edit an HTML file with half a dozen or more embedded lumps of SVG in there. It could quickly turn into an unreadable mess. And, as I already observed, <img> won’t work either. Ah, but AngularJS jumps to the fore again because it has it’s ng-include directive. All I had to do was this:

<span ng-include="'images/sunshine_plus_temp.svg'"></span>

and AngularJS was including the image where I needed it and binding the variable to the model for real-time update. Here’s the final version of the code I came up with for my first example, note the second set of quotes inside the ng-include to tell it not to interpret the string inside there, it’s just a string to use directly:

    <p>Example 1: Text updated on the fly in an SVG graphic via AngularJS.</p>
    <span ng-include="'images/sunshine_plus_temp.svg'"></span>
  <label>Temperature</label> <input type="text" ng-model="temp"/>

It’s worth noting that Inkscape is still perfectly capable of editing the SVG file even after the change I made and I guess I could have just made the change within Inkscape in the first place and never bothered opening up the file to manually change it with a text editor.

Inkscape editing modified SVG icon

Example 2: Have an SVG graphic that incorporates an image (just because it’s vector doesn’t mean it has to be all vector, SVG is great with images too) and use AngularJS to swap out the images on the fly.

We don’t really need a second example here, the first one showed pretty much everything but I wanted to show how easily images incorporate into SVG and help you achieve results that would be much much harder to do with other techniques. In this example I took a slides icon by Diego Naive, from The Noun Project, overlaid an image on top of it, and then overlaid a glossy reflection on top of half the slide, just to show that the image is fully incorporated by the graphic and can easily be rotated, have graphics on top of it, underneath it, etc. Stuff that would require a lot of work to do with many other techniques.

Again, I tested it out and edited the final SVG file to add a variable reference, in this case to {{slide_image}} instead of the specific file reference that I had added with Inkscape. This time, I will say that it does not edit nearly as well in Inkscape after the edit because it doesn’t know where to find an image named “{{slide_image}}”. Within the Inkscape editor you just see an error box where the image should be. Not perfect, but not debilitating either.

Here’s a page with links to both examples and to the Github repository with all the code for both: http://johnmunsch.github.io/AngularJSExamples/

Can you do JavaScript development with just an iPad at hand?

I recently headed off on a five day vacation and though I do have my priorities in order (eat, see the sights, take photos, walk a lot, read a lot) there is inevitably some downtime as the days go on. I didn’t want to lug along a laptop on this vacation so I resolved to see if there was any practical way to play with AngularJS and Ember.js (two frameworks I’ve been interested in recently) using only my iPad and an inexpensive Bluetooth keyboard.*

iPad and Bluetooth keyboard

For those who wish to skip ahead, the short answer is that it is possible, but it’s not much fun figuring it out so I’ll tell you later how I did it. As for whether it’s practical, I don’t think I’d consider it for anything except a small test project and the reason why comes down to one simple thing: debugging. If you’re a modern JavaScript developer you’re used to wonderful tools like Firebug and the Chrome Developer Tools for debugging and while Safari on iOS once had access to some basics like the JavaScript console those have been removed from iOS 6 in favor of a new remote debugging method. The new solution relies on a remote connection to Safari on Mac OS X. I’m sure it’s a much more sophisticated solution but why did we need to lose all JavaScript debugging support on iOS to get it? If I have to have my Mac along to do debugging I might as well do the JavaScript work on OS X in the first place…

That leaves your only debugging option as Firebug Lite 1.4, a project which has basically been abandoned due to lack of funds or interest or something and when I tried to combine it with AngularJS I was never able to get it to appear within the browser. I had more success with Ember.js because it both appeared and showed all the console messages from Ember, however the script tab was unable to show me the contents of any of the JavaScript files I was including locally. Due to the slow performance of the wi-fi at my hotel I pulled firebug-lite.js, jquery, handlebars, ember, etc. all down to my iPad and put them in the same location as the index.html file and the main.js file I was editing. Due to some form of security restriction with how the files were being loaded into the local browser Firebug Lite was unable to show any of them to me.


That means that you’re going to be flying completely blind with AngularJS unless you’re prepared to handle logging via some other mechanism and even on Ember.js, are we really looking forward to something that’s reduced us to debugging entirely via log messages?


I promised that I would say what I found worked best for development work and it was Textastic. It will let you create directories, fill them with files, edit them, and then view them with a built in instance of the iOS browser. It’s simple and straightforward and I was able to paste in sample AngularJS and Ember.js pages and they worked just great. I just couldn’t ever debug them properly. It does cost a few dollars but if you’re just looking for some easy way to play with HTML, CSS, or some simple JavaScript when all you have is an iPad (and hopefully a paired keyboard) then it’ll do in a pinch.

BTW, Cloud9 IDE looks like it would be an even better solution to this problem but they use the Ace editor and for whatever reason, it doesn’t work well on an iPad. I had problems with cursor position being one place while actual editing was another, it didn’t want to work well with my keyboard, it seemed slow, etc. There needs to be some work done on either the editor itself or on the iPad browser (or perhaps both) to make that a more viable solution.

Textastic - Ember.js plus Firebug LiteP.S. Most of this blog entry was written on the self same iPad/keyboard so don’t think the iPad is useless for any form of content creation, it just doesn’t do software development well at this time.

* Specifically a third generation iPad and the AmazonBasics Bluetooth Keyboard.