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# Friday, July 31, 2015

Taking into an account that we use Saxon for many years, it was strange to run into so simple error like the following:

<xsl:stylesheet version="2.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
  <xsl:template match="/">
    <xsl:variable name="doc" as="element()+"><a/><b/><c/></xsl:variable>   
    <xsl:sequence select="$doc = 3"/>
  </xsl:template>
</xsl:stylesheet>

This is a simplified case that should produce an dynamic error FORG0001 as per General Comparisions; the real code is more complex, as it uses SFINAE and continues.

This case crushes in Saxon with exception:

Exception in thread "main" java.lang.RuntimeException: 
      Internal error evaluating template  at line 3 in module ICE9.6.xslt
    at net.sf.saxon.expr.instruct.Template.applyLeavingTail()
    at net.sf.saxon.trans.Mode.applyTemplates()
    at net.sf.saxon.Controller.transformDocument()
    at net.sf.saxon.Controller.transform()
    at net.sf.saxon.s9api.XsltTransformer.transform()
    at net.sf.saxon.jaxp.TransformerImpl.transform()
    ...
Caused by: java.lang.NumberFormatException: For input string: "" 
    at java.lang.NumberFormatException.forInputString()
    at java.lang.Long.parseLong()
    at java.lang.Long.parseLong()
    at net.sf.saxon.expr.GeneralComparison.quickCompare()
    at net.sf.saxon.expr.GeneralComparison.compare()
    at net.sf.saxon.expr.GeneralComparison.evaluateManyToOne()
    at net.sf.saxon.expr.GeneralComparison.evaluateItem()
    at net.sf.saxon.expr.GeneralComparison.evaluateItem()
    at net.sf.saxon.expr.Expression.process()
    at net.sf.saxon.expr.instruct.Template.applyLeavingTail()
    ... 8 more

We have reported the problem at Saxon's forum, and as usual the problem was shortly resolved.

Friday, July 31, 2015 8:36:39 AM UTC  #    Comments [0] -
xslt
# Monday, July 27, 2015

Though ADO.NET and other ORM framworks like EntityFramework and Dapper support async pattern, you should remember that database drivers (at least all we know about) do not support concurrent db commands running against a single connection.

To see what we mean consider a bug we have recently identified. Consider a code:

await Task.WhenAll(
  newImages.
    Select(
      async image =>
      {
        // Load data from url.
        image.Content = await HttpUtils.ReadData(image.Url);

        // Insert image into the database.
        image.ImageID = await context.InsertImage(image);
      }));

The code runs multiple tasks to read images, and to write them into a database.

Framework decides to run all these tasks in parallel. HttpUtils.ReadData() has no problem with parallel execution, while context.InsertImage() does not run well in parallel, and is a subject of race conditions.

To workaround the problem we had to use async variant of a critical section. So the fixed code looks like this:

using(var semaphore = new SemaphoreSlim(1))
{
  await Task.WhenAll(
    newImages.
      Select(
        async image =>
        {
          // Load data from url.
          image.Content = await HttpUtils.ReadData(image.Url);

          await semaphore.WaitAsync();

          try
          {
            // Insert image into the database.
            image.ImageID = await context.InsertImage(image);
          }
          finally
          {
            semaphore.Release();
          }
        }));
}

So, in the async world we still should care about race conditions.

Monday, July 27, 2015 6:44:45 AM UTC  #    Comments [0] -
.NET | Thinking aloud | Tips and tricks
# Friday, July 10, 2015

Here we show two snall directives that help to build fixed menu bar in your angularjs application.

There are two ideas behind:

  1. Expose element's bounds into a scope for a manipulation (ui-bounds directive).
  2. Allow to react to scroll DOM event (ui-scroll directive).

Directive implementation is very simple. See bounds.html at GitHub.

The use cases are also trivial to unerstand and implement. Take a look at two of them.

  1. Fixed menu:
    <div ng-style="{paddingTop: headerBounds.height.toFixed() + 'px' }">
      <div style="position: fixed; z-index: 1; top: 0; width: 100%; background: menu" 
        ui-bounds="headerBounds">My header</div>
      <div>
        long content that produces a scroll bar.
      </div>
    </div>
  2. Synchronized scroll of table header
    <div style="width: 50em; overflow: hidden; background: pink">
      <div style="position: relative" 
        ng-style="{left: bodyBounds.left.toFixed() + 'px'}">header...<div>
    </div>
    <div style="width: 50em; height: 5em; overflow: auto; background: blue"
      ui-scroll>
      <div ui-bounds="bodyBounds">body...</div>
    </div>

You can see the demo at: nesterovsky-bros/angularjs-api/master/angularjs/bounds.html.

Friday, July 10, 2015 9:04:40 PM UTC  #    Comments [0] -
AngularJS | javascript
# Sunday, June 7, 2015

In our angularjs projects we are often dealing with existing models that do not always fit to angularjs expectations.

Here is an example.

There is a model consisting of two arrays: for data, and for associated data. How to create an ng-repeat that displays data from both sources?

Consider a test controller (see a github sources, and a rawgit working sample):

model.controller(
  "Test",
  function()
  {
    this.records =
    [
      { name: "record 1", state: "Draft" },
      { name: "record 2", state: "Public" },
      { name: "record 3", state: "Disabled" },
      { name: "record 4", state: "Public" },
      { name: "record 5", state: "Public" }
    ];

    this.more =
    [
      { value: 1, selected: true, visible: true },
      { value: 2, selected: false, visible: true },
      { value: 3, selected: true, visible: true },
      { value: 4, selected: false, visible: false },
      { value: 5, selected: false, visible: true }
    ];

    this.delete = function(index)
    {
      this.records.splice(index, 1);
      this.more.splice(index, 1);
    };
  });

Basically there are three approaches here:

  1. Change model.
  2. Adapt model to a single collection.
  3. ng-repeat over first array and access the second array using $index scope variable.

We argued like this:

  • It is often not an option to change a model, as it's how business data are described.
  • A model adaptation when we build a single collection from original two collections, and synchronize it back (if required) may unnecessary complicate things.
  • Thus let's get associated items by $index variable.

This is an example of ng-repeat use:

<table border="1">
  <tr>
    <th>[x]</th>
    <th>Name</th>
    <th>Value</th>
    <th>State</th>
    <th>Actions</th>
  </tr>
  <tr ng-repeat="item in test.records track by $index"
    ng-if="test.more[$index].visible">
    <td>    
      <input type="checkbox" ng-model="test.more[$index].selected"/>
    </td>
    <td>{{item.name}}</td>
    <td>{{test.more[$index].value}}</td>
    <td>{{item.state}}</td>
    <td>
      <a href="#" ng-click="test.delete($index)">Delete</a>
    </td>
  </tr>
</table>

Look at how associated data is accessed: test.more[$index]... Our goal was to optimize that repeating parts, so we looked at ng-init directive.

Though docs warn about its use: "the only appropriate use of ngInit is for aliasing special properties of ngRepeat", we thought that our use of ng-init is rather close to what docs state, so we tried the following:

...
<tr ng-repeat="item in test.records track by $index" 
  ng-init="more = test.more[$index]" 
  ng-if="more.visible">
  <td>    
    <input type="checkbox" ng-model="more.selected"/>
  </td>
  <td>{{item.name}}</td>
  <td>{{more.value}}</td>
  <td>{{item.state}}</td>
  <td>
    <a href="#" ng-click="test.delete($index)">Delete</a>
  </td>
</tr>
...

This code just does not work, as it shows empty table, as if ng-if is always evaluated to false. From docs we found the reason:

  • the priority of the directive ng-if is higher than the prirority of the ng-init, and besides ng-if is a terminal directive;
  • as result ng-if directive is bound, and ng-init is not;
  • when ng-if is evaluated no $scope.more is defined, so more.visible is evaluated to false.

To workaround ng-init/ng-if problem we refactored ng-if as ng-if-start/ng-if-end:

...
<tr ng-repeat="item in test.records track by $index" 
  ng-init="more = test.more[$index]">
  <td ng-if-start="more.visible">
    <input type="checkbox" ng-model="more.selected"/>
  </td>
  <td>{{item.name}}</td>
  <td>{{more.value}}</td>
  <td>{{item.state}}</td>
  <td ng-if-end>
    <a href="#" ng-click="test.delete($index)">Delete</a>
  </td>
</tr>
...

This code works much better and shows a correct content. But then click "Delete" for a row with Name "record 2" and you will find that updated table is out of sync for all data that come from test.more array.

So, why the data goes out of sync? The reason is in the way how the ng-init is implemented: its expression is evaluated just once at directive's pre-link phase. So, the value of $scope.more will persist for the whole ng-init's life cycle, and it does not matter that test.mode[$index] may have changed at some point.

At this point we have decided to introduce a small directive named ui-eval that will act in a way similar to ng-init but that:

  • will run before ng-if;
  • will be re-evaluated when it's value is changed.

This is it:

module.directive(
  "uiEval",
  function()
  {
    var directive =
    {
      restrict: 'A',
      priority: 700,
      link:
      {
        pre: function(scope, element, attr)
        {
          scope.$watch(attr["uiEval"]);
        }
      }
    };

    return directive;
  });

The ui-eval version of the markup is:

...
<tr ng-repeat="item in test.records track by $index" 
  ui-eval="more = test.more[$index]" 
  ng-if="more.visible">
  <td>    
    <input type="checkbox" ng-model="more.selected"/>
  </td>
  <td>{{item.name}}</td>
  <td>{{more.value}}</td>
  <td>{{item.state}}</td>
  <td>
    <a href="#" ng-click="test.delete($index)">Delete</a>
  </td>
</tr>
...

It works as expected both during initial rendering and when model is updated.

We consider ui-eval is a "better" ng-init as it solves ng-init's silent limitations. On the other hand it should not try to evaluate any complex logic, as it can be often re-evaluated, so its use case is to alias a sub-expression. It can be used in any context and is not limited to items of ng-repeat.

Source code can be found at github, and a working sample at rawgit.

Sunday, June 7, 2015 11:46:11 AM UTC  #    Comments [0] -
AngularJS | javascript | Tips and tricks
# Sunday, May 31, 2015

In one of our last projects we were dealing with audio: capture audio in browser, store it on server and then return it by a request and replay in browser.

Though an audio capturing is by itself rather interesting and challenging task, it's addressed by HTML5, so for example take a look at this article. Here we share our findings about other problem, namely an audio conversion.

You might thought that if you have already captured an audio in browser then you will be able to play back it. Thus no additional audio conversion is required.

In practice we are limited by support of various audio formats in browsers. Browsers can capture audio in WAV format, but this format is rather heavy for storing and streaming back. Moreover, not all browsers support this format for playback. See wikipedia for details. There are only two audio formats that more or less widely supported by mainstream browsers: MP3 and AAC. So, you have either convert WAV to MP3, or to AAC.

The obvious choice is to select WAV to MP3 conversion, the benefit that there are many libraries and APIs for such conversion. But in this case you risk falling into a trap with MP3 licensing, especially if you deal with iteractive software products.

Eventually, you will come to the only possible solution (at least for moment of writting) - conversion WAV to AAC.

The native solution is to use NAudio library, which behind the scene uses Media Foundation Transforms. You'll shortly get a working example. Actually the core of solution will contain few lines only:

var source = Path.Combine(root, "audio.wav");
var target = Path.Combine(root, "audio.m4a");

using(var reader = new NAudio.Wave.WaveFileReader(source))
{
  MediaFoundationEncoder.EncodeToAac(reader, target);
}

Everything is great. You'll deploy your code on server (by the way server must be Windows Server 2008R2 or higher) and at this point you may find that your code fails. The problem is that Media Foundation API is not preinstalled as a part of Windows Server installation, and must be installed separately. If you own this server then everything is all right, but in case you use a public web hosting server then you won't have ability to install Media Foundation API and your application will never work properly. That's what happened to us...

After some research we came to conclusion that another possible solution is a wrapper around an open source video/audio converter - FFPEG. There were two issues with this solution:

  • how to execute ffmpeg.exe on server asynchronously;
  • how to limit maximum parallel requests to conversion service.

All these issues were successfully resolved in our prototype conversion service that you may see here, with source published on github. The solution is Web API based REST service with simple client that uploads audio files using AJAX requests to server and plays it back. As a bonus this solution allows us perform not only WAV to AAC conversions, but from many others format to AAC without additional efforts.

Let's take a close look at crucial details of this solution. The core is FFMpegWrapper class that allows to run ffmpeg.exe asynchronously:

/// <summary>
/// A ffmpeg.exe open source utility wrapper.
/// </summary>
public class FFMpegWrapper
{
  /// <summary>
  /// Creates a wrapper for ffmpeg utility.
  /// </summary>
  /// <param name="ffmpegexe">a real path to ffmpeg.exe</param>
  public FFMpegWrapper(string ffmpegexe)
  {
    if (!string.IsNullOrEmpty(ffmpegexe) && File.Exists(ffmpegexe))
    {
      this.ffmpegexe = ffmpegexe;
    }
  }

  /// <summary>
  /// Runs ffmpeg asynchronously.
  /// </summary>
  /// <param name="args">determines command line arguments for ffmpeg.exe</param>
  /// <returns>
  /// asynchronous result with ProcessResults instance that contains 
  /// stdout, stderr and process exit code.
  /// </returns>
  public Task<ProcessResults> Run(string args)
  {
    if (string.IsNullOrEmpty(ffmpegexe))
    {
      throw new InvalidOperationException("Cannot find FFMPEG.exe");
    }

    //create a process info object so we can run our app
    var info = new ProcessStartInfo 
    { 
      FileName = ffmpegexe,
      Arguments = args,
      CreateNoWindow = true
    };

    return ProcessEx.RunAsync(info);
  }

  private string ffmpegexe;
}

It became possible to run  a process asynchronously thanks to James Manning and his ProcessEx class.  

Another useful part is a semaphore declaration in Global.asax.cs:

   public class WebApiApplication : HttpApplication
  {
    protected void Application_Start()
    {
      GlobalConfiguration.Configure(WebApiConfig.Register);
    }

    /// <summary>
    /// Gets application level semaphore that controls number of running 
    /// in parallel FFMPEG utilities.
    /// </summary>
    public static SemaphoreSlim Semaphore
    {
      get { return semaphore; }
    }

    private static SemaphoreSlim semaphore;

    static WebApiApplication()
    {
      var value =
        ConfigurationManager.AppSettings["NumberOfConcurentFFMpegProcesses"];

      int intValue = 10;

      if (!string.IsNullOrEmpty(value))
      {
        try
        {
          intValue = System.Convert.ToInt32(value);
        }
        catch
        {
          // use the default value
        }
      }

      semaphore = new SemaphoreSlim(intValue, intValue);
    }
  }

And the last piece is the entry point, which was implemented as a REST controller:

/// <summary>
/// A controller to convert audio.
/// </summary>
public class AudioConverterController : ApiController
{
  /// <summary>
  /// Gets ffmpeg utility wrapper.
  /// </summary>
  public FFMpegWrapper FFMpeg
  {
    get
    {
      if (ffmpeg == null)
      {
        ffmpeg = new FFMpegWrapper(
          HttpContext.Current.Server.MapPath("~/lib/ffmpeg.exe"));
      }

      return ffmpeg;
    }
  }

  /// <summary>
  /// Converts an audio in WAV, OGG, MP3 or other formats 
  /// to AAC format (MP4 audio).
  /// </summary>
  /// <returns>A data URI as a  string.</returns>
  [HttpPost]
  public async Task<string> ConvertAudio([FromBody]string audio)
  {
    if (string.IsNullOrEmpty(audio))
    {
      throw new ArgumentException(
        "Invalid audio stream (probably the input audio is too big).");
    }

    var tmp = Path.GetTempFileName();
    var root = tmp + ".dir";

    Directory.CreateDirectory(root);
    File.Delete(tmp);

    try
    {
      var start = audio.IndexOf(':');
      var end = audio.IndexOf(';');
      var mimeType = audio.Substring(start + 1, end - start - 1);
      var ext = mimeType.Substring(mimeType.IndexOf('/') + 1);
      var source = Path.Combine(root, "audio." + ext);
      var target = Path.Combine(root, "audio.m4a");

      await WriteToFileAsync(audio, source);

      switch (ext)
      {
        case "mpeg":
        case "mp3":
        case "wav":
        case "wma":
        case "ogg":
        case "3gp":
        case "amr":
        case "aif":
        case "mid":
        case "au":
        {
          await WebApiApplication.Semaphore.WaitAsync();

          var result = await FFMpeg.Run(
            string.Format(
              "-i {0} -c:a libvo_aacenc -b:a 96k {1}",
              source,
              target));

          WebApiApplication.Semaphore.Release();

          if (result.Process.ExitCode != 0)
          {
            throw new InvalidDataException(
              "Cannot convert this audio file to audio/mp4.");
          }

          break;
        }
        default:
        {
          throw new InvalidDataException(
            "Mime type: '" + mimeType + "' is not supported.");
        }
      }

      var buffer = await ReadAllBytes(target);
      var response = "data:audio/mp4;base64," + System.Convert.ToBase64String(buffer);

      return response;
    }
    finally
    {
      Directory.Delete(root, true);
    }
  }

For those who'd like to read more about audio conversion, we may suggest to read this article.

Sunday, May 31, 2015 10:32:21 AM UTC  #    Comments [0] -
.NET | ASP.NET
# Thursday, May 7, 2015

Stackoverfow shows that people are searching How to intercept $resource requests.

Recently we have written about the way to cancel angularjs $resource requests (see Cancel angularjs resource request). Here we apply the same technique to intercept resource request.

Consider a sample (nesterovsky-bros/angularjs-api/master/angularjs/transform-request.html):

<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8" />
  <title>Intercept resource request</title>
  <style type="text/css">.ng-cloak { display: none; }</style>
  <script src="angular.js"></script>
  <script src="angular-resource.js"></script>
  <script>
angular.module("app", ["ngResource"]).
  factory(
    "services",
    ["$resource", function ($resource)
    {
      return $resource(
        "http://md5.jsontest.com/",
        {},
        {
          MD5:
          {
            method: "GET",
            params: { text: null },
            then: function (resolve)
            {
              this.params.text = "***" + this.params.text + "***";
              this.then = null;
              resolve(this);
            }
          },
        });
      }]).
  controller(
    "Test",
    ["services", function (services)
    {
      this.value = "Sample text";

      this.call = function()
      {
        this.result = services.MD5({ text: this.value });
      }
    }]);
  </script>
</head>
<body ng-app="app" ng-controller="Test as test">
  <label>Text: <input type="text" ng-model="test.value" /></label>
  <input type="button" value="call" ng-click="test.call()"/>
  <div ng-bind="test.result.md5"></div>
</body>
</html>

How it works.

  1. $resource merges action definition, request params and data to build a config parameter for an $http request.
  2. a config parameter passed into an $http request is treated as a promise like object, so it may contain then function to initialize config.
  3. action's then function may transform request as it wishes.

The demo can be found at transform-request.html

Thursday, May 7, 2015 10:53:34 AM UTC  #    Comments [0] -
AngularJS | javascript | Tips and tricks
# Monday, May 4, 2015

Having a strong experience in ASP.NET and JSF, we found angular's transclusion concept is obscure and counterintuitive. It took a while for both of us to grasp the transclude's ideas described the Developer Guide. We suspect that this is due to the bad design: a bad design leads to a bad wording.

The other consequence of the bad design is that the transclusion is limited to one template per directive, which limits the use of the feature.

Consider:

  • A directive my-page that encapsulates a page with menu and content.
  • my-page uses templateUrl: my-page.html to render the page.
  • my-page.html defines two sites where menu and page content have to be embedded.
  • Two content fragments are passed to my-page to fill content sites.

Unfortunately, you cannot immediately implement this design in angularjs. On the other hand ASP.NET's Master Pages, and JSF's ui:composition readily solve this task.

Here is one of JSF's approaches:

  1. Define page template my-page.xhtml:
    <html xmlns="http://www.w3.org/1999/xhtml"
      xmlns:ui="http://java.sun.com/jsf/facelets"
      xmlns:h="http://java.sun.com/jsf/html">
      <h:body>
        <table>
          <tr>
            <td><ui:insert name="menu"/></td>
          </tr>
          <tr>
            <td><ui:insert name="content"/></td>
          </tr>
        </table>
      </h:body>
    </html>
  2. Use ui:composition tag to pass parts to the template:
    <html xmlns="http://www.w3.org/1999/xhtml"
      xmlns:ui="http://java.sun.com/jsf/facelets"
      xmlns:h="http://java.sun.com/jsf/html">
      <h:body>
        <ui:composition template="my-page.xhtml">
          <ui:define name="content">
            My Content
          <ui:define>
          <ui:define name="menu">
            <a href="#file">File</a>
            <a href="#edit">Edit</a>
            <a href="#view">View</a>
          <ui:define>
        </ui:composition>
      </h:body>
    </html>

We have decided to model angular directives after JSF, and have defined three simple directives: ui-template, ui-insert, ui-define (see angularjs-api/template/ui-lib.js).

To define a template one writes the following markup (see angularjs-api/template/my-page.html):

<table ui-template>
  <tr>
    <td ui-insert="menu"></td>
  </tr>
  <tr>
    <td ui-insert="content"></td>
  </tr>
</table>

and declares a directive (see angularjs-api/template/my-page.js):

var myPage =
{
  templateUrl: "my-page.html",
  transclude: true
};

angular.module("app").
  directive("myPage", function() { return myPage; });

and finally, to instantiate the directive one needs to write (see angularjs-api/template/sample.html):

<my-page>
  <div ui-define="content">
    My content
  </div>
  <div ui-define="menu">
    <a href="#file">File</a>
    <a href="#edit">Edit</a>
    <a href="#view">View</a>
  </div>
</my-page>

The working sample can be seen through rawgit: sample.html

The other sample that integrates with routing can be found at sample-routing.html

Monday, May 4, 2015 1:07:53 PM UTC  #    Comments [0] -
AngularJS | javascript | Thinking aloud
# Thursday, April 9, 2015

After ECMAScript Xml Object Model we aligned JXOM to support Java 8. This includes support of:

As with ECMAScript, all sources are available at https://github.com/nesterovsky-bros/languages-xom

Thursday, April 9, 2015 7:46:22 PM UTC  #    Comments [0] -
Announce | Java | xslt
# Monday, April 6, 2015

Much time has passed since we fixed or extended Languages Xml Object Model. But now we needed to manipulate with and generate javascript programs.

Though xslt today is not a language of choice but rather niche language, it still fits very well to tasks of code generation and transformation.

So, we're pleased to announce ECMAScript Xml Object Model, which includes:

All sources are available at github: https://github.com/nesterovsky-bros/languages-xom

Monday, April 6, 2015 12:17:04 PM UTC  #    Comments [0] -
Announce | javascript | xslt
# Sunday, March 22, 2015

A year ago we had published out attempt at creating WeakTable in .NET. This is not too often used API but at rare case it's just irreplaceable.

But yesterday a user @Paya has finally found our class to be useful, performed the code review, and identified some bugs. See discussion at StackOverflow.

Bug fixes are available at: https://github.com/nesterovsky-bros/WeakTable.

Sunday, March 22, 2015 8:05:29 AM UTC  #    Comments [0] -
.NET | Announce
# Wednesday, March 18, 2015

Two years ago, when we were still actively using KendoUI we had published our approach on how to introduce custom widgets, which we called User Controls.

We even suggested to introduce UserControl widget into KendoUI core through feedback page. At that time we got a response from KendoUI team:

Our recommended approach for building reusable app building blocks is expressed via the Kendo UI SPA features delivered earlier this year. Here’s a getting started resource if you’ve not already seen it: http://www.kendoui.com/blogs/teamblog/posts/13-05-16/kendo-ui-spa-screencast-and-getting-started.aspx

It was not clear how the response is related to the suggestion, but we decided not to rebuke the team, and to proceed with our user controls.

Nowdays we use KendoUI no more, and have completely switched to angularjs. Ocasionally, however, we need to support old projects, and peek into docs. Today we've discovered that the team has changed their mind, and allowed custom widgets: "Create Your Own Kendo UI Widget by Inheriting from the Base Widget Class". That's good news!

But the most interesting thing is that the design of their custom widget is very close to what we have suggested then.

Wednesday, March 18, 2015 2:16:25 PM UTC  #    Comments [0] -
AngularJS | javascript | kendoui
# Saturday, March 14, 2015

Angularjs is reasonaly good library but as many other big frameworks it tries to absorb every role in itself. This leads to code bloat of the framework and often limits developers with API available.

This problem repeats in angularjs on different levels. The top manifistation is module system.

Authors defined notion of module and registry for controllers, providers, directives, and so on. This is an example from Angularjs doc:

var myModule = angular.module('myModule', []);

// add some directives and services
myModule.service('myService', ...);
myModule.directive('myDirective', ...);

This API directs developers to build angularjs centric applications, because it's where module and registry is defined.

At the same time there exists de-facto standard API called Asynchronous Module Definition (AMD) to specify a mechanism for defining modules and their dependencies. This API has several implementations, where requirejs is, probably, the best known one. This is an AMD example:

define(["./cart", "./inventory"], function(cart, inventory) {
  return {
    color: "blue",
    size: "large",
    addToCart: function() {
      inventory.decrement(this);
      cart.add(this);
    }
  }
});

Every angularjs artifact can be mapped to AMD module. This could work equally well both at run time, and during unit tests. Without custom module implementation angularjs would be smaller, and more modular, so developer could pick up only required components. At the same time with AMD angularjs could treat many existing javascript classes as controllers and services without specific adaptation. Again, being more modular angularjs could provide multiple implementations of the same feature like jqLite vs jQuery, or $q vs native promises, for a developer to select.

So, we think modules in angularjs is a flaw, whose correction would improve it in many ways.

Saturday, March 14, 2015 10:01:39 PM UTC  #    Comments [0] -
AngularJS | javascript
# Monday, February 2, 2015

We needed to cancel angularjs $resource requests but have found that it's not trivial, though $http service has timeout property that allows to pass a promise that aborts a request when resolved.

So, we took a little time and divised a code to be able to cancel such requests.

Consider a sample (nesterovsky-bros/angularjs-api/master/angularjs/cancel-resource.html):

<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8" />
  <title>Cancel resource</title>
  <style type="text/css">
    .ng-cloak { display: none; }
  </style>
  <script src="angular.js"></script>
  <script src="angular-resource.js"></script>
  <script>
angular.module("app", ["ngResource"]).
factory(
  "services",
  ["$resource", function($resource)
  {
    function resolveAction(resolve) // #1
    {
      if (this.params)
      {
        this.timeout = this.params.timeout;
        this.params.timeout = null;
      }

      this.then = null;
      resolve(this);
    }

    return $resource(
      "http://md5.jsontest.com/",
      {},
      {
        MD5:
        {
          method: "GET",
          params: { text: null },
          then: resolveAction // #2
        },
      });
  }]).
controller(
  "Test",
  ["services", "$q", "$timeout", function(services, $q, $timeout)
  {
    this.value = "Sample text";
    this.requestTimeout = 100;

    this.call = function()
    {
      var self = this;

      self.result = services.MD5(
      {
        text: self.value,
        timeout: $q(function(resolve) // #3
        {
          $timeout(resolve, self.requestTimeout);
        })
      });
    }
  }]);
  </script>
</head>
<body ng-app="app" ng-controller="Test as test">
  <label>Text: <input type="text" ng-model="test.value" /></label><br/>
  <label>Timeout: <input type="text" ng-model="test.requestTimeout" /></label><br/>
  <input type="button" value="call" ng-click="test.call()"/>
  <div ng-bind="test.result.md5"></div>
</body>
</html>  

How it works.

  1. $resource merges action definition, request params and data to build a config parameter for an $http request.
  2. a config parameter passed into an $http request is treated as a promise like object, so it may contain then function to initialize config.
  3. action's then function may pass timeout promise from params into the config.

In code it looks like this:

  • #2 - here we attach then function to the action MD5;
  • #1 - then function implementation:
    • move timeout promise, if any, from params to config;
    • reset then function from config to prevent resolve recursion (remember that we deal with merged config object, which is different from action definition);
    • call resolve function.
  • #3 - While calling services.MD5() we pass a timeout parameter as a promise that should be resolved to abort the request.

That's all. The demo can be found at cancel-resource.html

Monday, February 2, 2015 11:05:36 AM UTC  #    Comments [0] -
AngularJS | javascript
# Monday, January 26, 2015

Often we need to keep a client session state in our angularjs application.

This state should survive page refresh and navigations within the application.

Earlier we used ngStorage module but lately have changed our opinion, as we think it's over-engineered and is too heavy at runtime.

We have replaced it with a simple service that synchronizes sessionStorage once during initialization, and once before page unload.

Look at an example (session.html):

<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8" />
  <title>Session</title>
  <style type="text/css">
    .ng-cloak { display: none; }
  </style>
  <script src="angular.js"></script>
  <script>
angular.module("app", []).
factory(
  "session",
  ["$window", function($window)
  {
    var session =
      angular.fromJson($window.sessionStorage.getItem("app")) || {};

    $window.addEventListener(
      "beforeunload",
      function()
      {
        $window.sessionStorage.setItem("app", angular.toJson(session));
      })

    return session;
  }]).
controller(
  "Test",
  ["session",
  function(session)
  {
    this.state = session;
  }]);
  </script>
</head>
<body ng-app="app" ng-controller="Test as test">
  <input type="text" ng-model="test.state.value"/>
  <a href="session.html?p=1">Page 1</a>
  <a href="session.html?p=2">Page 2</a>
</body>
</html>    

Source can be found at nesterovsky-bros/angularjs-api/services/session.html.

Monday, January 26, 2015 8:46:36 AM UTC  #    Comments [2] -
AngularJS | javascript | Tips and tricks
# Sunday, January 18, 2015

At first we have found that Typeahead (ui.bootstrap.typeahead) directive fits our needs, but later we run into its limitations.

These are tasks we required to solve:

  1. How to inform typeahead directive that it should update its list based on some event?
  2. How to implement an array of typeahead sources, where it's assumed that each next source delivers more data in cost of a longer working time?

The second task allows to show some data in popup almost immediately, while to provide more hints lately.

It took us a couple of days to answer both questions. The solution was either to write "typeahead" directive anew, or to write some additional "typeahead" directive to implement missing functionality. We have selected the later.

In the additional directive we:

  1. Handle a scople level event named "updateSource". Once the event is triggered the popup content is updated.
  2. Introduces scope.sources = function(value, sourcesFn) to build a source promise that knows how to update popup with more accurate data, when available.

Here is the code with small sample:

<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8" />
  <title>Typeahead</title>
  <link type="text/css" rel="stylesheet" href="bootstrap.css" />
  <style type="text/css">
    .ng-cloak { display: none; }
  </style>
  <script src="angular.js"></script>
  <script src="ui-bootstrap-tpls-0.12.0.js"></script>
  <script>
angular.module("app", ["ui.bootstrap"]).
directive(
  "typeahead",
  ["$q", function ($q)
  {
    return (
    {
        require: 'ngModel',
        link: function(scope, element, attrs, controller)
        {
          /**
           * @description 
           * Emits "updateSource" event on this scope.
           * @returns an event.
           */
          scope.updateSource = function() 
          { 
            return scope.$emit("updateSource"); 
          };

          scope.$on(
            "updateSource",
            function(event)
            {
              if (scope != event.targetScope)
              {
                return;
              }

              if (element.attr("aria-expanded") !== "true")
              {
                event.preventDefault();

                return;
              }

              var value = controller.$modelValue;

              for(var i = 0; i < controller.$parsers.length; i++)
              {
                if (value === undefined)
                {
                  break;
                }

                value = controller.$parsers[i](value);
              }
            });

          var typeaheadSources = null;
          var typeaheadValue = null;
          var typeaheadResult = null;

          /**
            * A wrapper of array of sources, where it's assumed that each next 
            * source delivers more data in cost of a longer working time.
            *
            * @param {object} value a typeahead hint.
            *
            * @param {function(object)} sourcesFn Function receiving typeahead
            *   hint, and returning an array of {Object|Promise}.
            *   If Object is passed rather than Promise then it should contain 
            *   following properties:
            *
            *    - `promise` - `{Promise}` - a result promise.
            *    - `cancel` - `{function()}` - optional function to cancel 
            *                 the promise.
            */
          scope.sources = function(value, sourcesFn)
          {
            var result = typeaheadResult;
            var prevValue = typeaheadValue;

            typeaheadValue = controller.$modelValue;
            typeaheadResult = null;

            if (result && (prevValue === typeaheadValue))
            {
              return result;
            }

            var sources = typeaheadSources;

            function cancel(count)
            {
              for (var i = 0; i < count; ++i)
              {
                var source = sources[i];

                source.cancel && source.cancel();
              }
            }

            sources && cancel(sources.length);
            typeaheadSources = sources = sourcesFn(value);

            return $q(function(resolve)
            {
              sources.forEach(function(source, index)
              {
                var promise = source.then ? source :
                  source.promise ? source.promise :
                  $q.when(source);

                promise.then(function(result)
                {
                  if (sources != typeaheadSources)
                  {
                    cancel(sources.length);

                    return;
                  }

                  if (element[0] != document.activeElement)
                  {
                    cancel(sources.length);
                    typeaheadSources = null;

                    return;
                  }

                  cancel(index);

                  if (!result || !result.length)
                  {
                    return;
                  }

                  if (resolve)
                  {
                    resolve(result);
                    resolve = null;
                  }
                  else
                  {
                    typeaheadResult = result;

                    if (scope.updateSource().defaultPrevented)
                    {
                      cancel(sources.length);
                      typeaheadSources = null;
                      typeaheadResult = null;
                      typeaheadValue = null;
                    }
                  }
                });
              });
            });
          }
        }
    });
  }]).
controller(
  "Test",
  ["$timeout",
  function ($timeout)
  {
    this.text = null;
    this.input = null;

    function source(timeout, count, value)
    {
      return (
      {
        promise: $timeout(
          function()
          {
            var result = [];

            for(var i = 0; i < count; ++i)
            {
              result.push({ text: value + " " + i, id: i });
            }

            return result;
          },
          timeout),

        cancel: function() { $timeout.cancel(this.promise); }
      });
    }

    // Gets an array of objects in format: 
    //   { promise: Promise, cancel: Function }
    this.suggest = function(value)
    {
      return [source(500, 5, value), source(2000, 10, value)];
    }
  }]);
  </script>
</head>
<body ng-app="app" ng-controller="Test as test">
  <input type="text"
    ng-model="test.text"
    typeahead="items.text for items in sources($viewValue, test.suggest)"
    typeahead-wait-ms="250"/><br />
  <input type="text" ng-model="test.input" />
</body>
</html>
    

Demo can be found at typeahead.html, and source at nesterovsky-bros/angularjs-api/bootstrap/typeahead.html.

Sunday, January 18, 2015 8:50:56 PM UTC  #    Comments [0] -
AngularJS | javascript
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