August 12, 2015

AngularJS - Logging Client Side Stack Trace

August 12, 2015/ John Liu

Nothing beats mythical errors that happens on the client side, but not on your development machine.

This post follows yesterday's post on configuring AngularJS to catch and log exceptions back to the server via an AJAX request.

Logging the Exception

Quick recap of the logging error handler.

function error(message, data, title) {
  var $http = angular.injector(['ng']).get('$http');

  data['url'] = document.location.href;

  var request = {
    method : 'POST',
    url: _spPageContextInfo.webServerRelativeUrl + '/_layouts/MyService.svc/LogMessage',
    data: {
      'log': message,
      'meta': angular.toJson(data),
      'evt': 'error'
    },
    dataType: "json",
    headers: {
      "Content-Type": "application/json; charset=utf-8"
    }
  };
  var promise = $http(request);            

  promise['catch'](function(){
    // send to console log if can't log to webservice
    $log.error('Error: ' + message, data);
  });
}

{
  "exception":
  {
    "message":"[NG-Modular Error] Unable to get property 'Client' of undefined or null reference",
    "description":"Unable to get property 'Client' of undefined or null reference",
    "number":-2146823281
  },
  "url":"http://server/_layouts/MY/form.aspx?IsDlg=1&id=3#/client"
}

Yay it's logging. But actually, it's pretty hard to figure out where the error is coming from. "What we need", says the developer to the tester, "is the stack trace. If we have the stack trace we'd be able to repo this and fix it."

stacktraceJS

Grab: https://github.com/stacktracejs/stacktrace.js/blob/stable/stacktrace.js

function error(message, data, title) {
  var $http = angular.injector(['ng']).get('$http');
  
  // work out the stacktrace
  var stack = printStackTrace({e: data, guess: true});
  data['stack'] = stack;
  // attach to the logged data

  data['url'] = document.location.href;

  var request = {
    //...
  };
  var promise = $http(request);            
}

The following JSON gets logged.

{
  "exception":
  {
    "message":"[NG-Modular Error] Unable to get property 'exist' of undefined or null reference",
    "description":"Unable to get property 'exist' of undefined or null reference",
    "number":-2146823281
  },
  "url":"http://server/_layouts/MY/form.aspx?IsDlg=1&id=138#/",
  "stack":
  [
    "{anonymous}(#object,\"other\")",
    "printStackTrace(#object)",
    "error(\"[NG-Modular Error] Unable to get property 'exist' of undefined or null reference\",#object)",
    "{anonymous}(?)",
    "{anonymous}(#function)",
    "{anonymous}(#object)",
    "{anonymous}(#object)",
    "{anonymous}(?)"
  ]
} 

Tweaks

"Those #function and #object, they look pretty stupid." commented the developer, who now has the stacktrace, but still thinks it doesn't help all that much.

A few hacks to stacktrace.js

if (arg.constructor === Object) {
  //result[i] = '#object';
  result[i] = arg.constructor.toString();
}
...
else {
   //result[i] = '?';
   result[i] = arg.constructor.toString();
}

This gives more readable stacktrace:

{
  "exception":
  {
    "message":"[NG-Modular Error] Unable to get property 'exist' of undefined or null reference",
    "description":"Unable to get property 'exist' of undefined or null reference",
    "number":-2146823281
  },
  "stack":
  [
    "{anonymous}(\nfunction Object() {\n    [native code]\n}\n,\"other\")",
    "printStackTrace(\nfunction Object() {\n    [native code]\n}\n)",
    "error(\"[NG-Modular Error] Unable to get property 'exist' of undefined or null reference\",\nfunction Object() {\n    [native code]\n}\n)",
    "{anonymous}(TypeError)",
    "{anonymous}(#function)",
    "{anonymous}(\nfunction Object() {\n    [native code]\n}\n)",
    "{anonymous}(\nfunction Object() {\n    [native code]\n}\n)",
    "{anonymous}([object Event])"
  ],
  "url":"http://server/_layouts/MY/form.aspx?IsDlg=1&id=138#/"
}

Future of stacktraceJS

The latest version of StacktraceJS (as of August 2015) is marching towards a full promise/A pattern where you request the stacktrace, and it returns you a promise. Then promise resolves to an array of stack frames, which you can then pretty-print to your own liking.

var callback = function(stackframes) {
    var stringifiedStack = stackframes.map(function(sf) { 
        return sf.toString(); 
    }).join('\n'); 
    console.log(stringifiedStack); 
};
var errback = function(err) { console.log(err.message); };
StackTrace.get().then(callback, errback)

Expect the syntax to change, soon.

I'm also assuming for modern browsers, it'll even look into requesting SourceMap files for minified versions of JavaScript/TypeScript and resolve those lines in the stacktrace produced. Currently though, it doesn't do all those things. What it does manage so far, cross browser, is already fairly impressive and a great starting point.

August 11, 2015

AngularJS $http and logger Circular Dependency

August 11, 2015/ John Liu

Error

[$injector:cdep] Circular dependency found: $rootScope <- $http <- logger <- $exceptionHandler <- $rootScope <- $location <- routehelper

TLDR:

If you are looking for RequireJS's easy way to late-bind a dependency, here's how you do it in AngularJS.

var $http = angular.injector(['ng']).get('$http');

Story

I imagine this could be a fairly common scenario.

You implemented AngularJS, with a logger service.

 angular
     .module('blocks.logger')
     .factory('logger', logger);

 logger.$inject = ['$log'];
 function logger($log) {
        var service = {
            error   : error,
            log     : $log.log
        };
        return service;

        /////////////////////

        function error(message, data, title) {
            $log.error('Error: ' + message, data);
        }
}

You want to try to catch errors and log it back to your webservice
So add a REST call.

logger.$inject = ['$log', '$http'];
function logger($log, $http) {
    // snip.

    function error(message, data) {
        $log.error('Error: ' + message, data);

        var request = {
            method : 'POST',
            url: _spPageContextInfo.webServerRelativeUrl + '/_layouts/MyLogService.svc/LogMessage',
            data: {
                'log': message,
                'event': 'error',
                'meta': angular.toJson(data)
            },
            dataType: "json",
            headers: {
                "Content-Type": "application/json; charset=utf-8"
            }
        };
        $http(request);           
    }
}

Error!

[$injector:cdep] Circular dependency found: $rootScope <- $http <- logger <- $exceptionHandler <- $rootScope <- $location <- routehelper

I actually quite like this error. It's telling me the dependency tree starting from routehelper and looping around to $rootScope

Bingle will tell you to re-architect your solution so you have proper separation of concerns. But to be honest, I just want to log an error…

So here's how you do it.

var ng = angular.injector(['ng']);
var $http = ng.get('$http');

Final Code Summary

logger.$inject = ['$log'];
function logger($log) {
    // snip.

    function error(message, data) {
        $log.error('Error: ' + message, data);
        
        // inject $http here.
        var $http = angular.injector(['ng']).get('$http');
        if (!$http) return;
            var request = {
                method : 'POST',
                url: _spPageContextInfo.webServerRelativeUrl + '/_layouts/MyLogService.svc/LogMessage',
                data: {
                    'log': message,
                    'event': 'error',
                    'meta': angular.toJson(data)
                },
                dataType: "json",
                headers: {
                    "Content-Type": "application/json; charset=utf-8"
                }
            };
            $http(request);           
        }
}

July 30, 2015

PhantomJS and Office 365 Brisbane

July 30, 2015/ John Liu

I thoroughly enjoyed my trip up to Brisbane. I got to see some friends, saw my sister and presented PhantomJS with SharePoint and SharePoint Online.

The response was tremendous, those that came to my session seems really interested and gave me more ideas for future discussions.

The presentation and demo are here

The new business case scenarios:

Automated Smoke Testing of sites - randomly check pages and DOM exist - "nothing has so far blown up"
Smoke Testing of sites with different credentials!
Scanning and scrapping text off dynamic (Single Page Application) pages and feed them to SharePoint's Search Indexing Service. Thus, you can have textual search linking back to dynamic URLs.

I also really enjoyed Elaine's session on SharePoint 2016.

The next Office 365 Saturday in Australia will be in Melbourne. The registration is up here:

http://www.o365saturdayaustralia.com/melbourne

July 23, 2015

AngularJS Extend and Computed Property

July 23, 2015/ John Liu

This is an Intermediate level discussion on AngularJS Extend, Computed Property in general, and a fairly complicated binding bug that needs some new learning.

I came from a KnockoutJS world. In the KnockoutJS world which I'm familiar with, there is the concept of a Computed Property.

KnockoutJS Computed Property

Because native Javascript objects does not raise OnPropertyChanged events, KnockoutJS wraps properties with an observable wrapper.
A class would look like this:

function PersonViewModel(){
  var self = this;
  
  self.firstName = ko.observable("");
  self.lastName = ko.observable("");
  
  self.fullName = ko.computed(function(){
    return [
      ko.unwrap(self.firstName), 
      ko.unwrap(self.lastName)
    ].join(" ");
  });
}

The developer takes care of the properties firstName and lastName, and KnockoutJS understands when firstName or lastName changes, fullName needs to be re-evaluated.

AngularJS binds Native Javascript Object

In AngularJS, there is no direct concept of a Computed Property, instead, AngularJS watches various binding expressions and automatically re-evaluate expressions. Since AngularJS binds to native Javascript directly, it employs a dirty checking mechanism.

A native person might look like this:

var person = {
  firstName: "",
  lastName: ""
};

And a View would look like this:

<div>
  First Name: {{ person.firstName }}
  Last Name: {{ person.lastName }}
  Full Name: {{ person.firstName + ' ' + person.lastName }}
</div>

Defining Class for AngularJS

But very quickly, one would find that this gets very unwieldy, and you end up duplicating expressions everywhere in your View. Duplicated code is never good. So we need to tidy up the definition of the model a bit more.

function Person(){
  var self = this;
  
  self.firstName = "";
  self.lastName = "";
  
  self.fullName = function(){
    return [self.firstName,self.lastName].join(" ");
  };
}

AngularJS Extend

Such definitions are nice and good, but you will need a way to populate these when you pull your data back from a REST service as JSON. Luckily, AngularJS provides both angular.extend as well as angular.merge helper methods to get you going quickly.

If you are familar with jQuery, this is nearly identical to jQuery.extend, it copies the properties from the later objects onto the first one.

var jsonJohn = { firstName: "John", lastName: "Liu" };
var personJohn = angular.extend( new Person(), jsonJohn );

// personJohn should have firstName, lastName 
// and fullName() == 'John Liu'

The updated View is then:

<div>
  First Name: {{ person.firstName }}
  Last Name: {{ person.lastName }}
  Full Name: {{ person.fullName() }}
</div>

Extending Arrays

When you have a collection of people, the code needs to look like this:

var people = [];
var jsonPeople = [
  { firstName: "John", lastName: "Liu" },
  { firstName: "Mark", lastName: "Liu" }
];
people = angular.extend( people, jsonPeople );

<div data-ng-repeat="person in people">
  First Name: {{ person.firstName }}
  Last Name: {{ person.lastName }}
  Full Name: {{ person.fullName() }}
</div>

This looks good initially, except there are a few problems:

angular.extend does not know anything about Person class, and fullName is not available

var people = [
  new Person(),
  new Person()
];
var jsonPeople = [
  { firstName: "John", lastName: "Liu" },
  { firstName: "Mark", lastName: "Liu" }
];
people = angular.extend( people, jsonPeople );

angular.extend will override people[0] with jsonPeople[0] (not null). So the result still does not define fullName()

So you need something like this:

var people = [
  new Person() // always show one row by default even if blank
];
var jsonPeople = [
  { firstName: "John", lastName: "Liu" },
  { firstName: "Mark", lastName: "Liu" }
];
var l = jsonPeople.length > people.length ? jsonPeople.length : people.length;
for (var i=0; i < l; i++){
  people[i] = angular.extend( new Person(), people[i], jsonPeople[i] );
  // copy jsonPeople[i] (if not null) onto people[i]
  // copy people[i] onto new Person()
  // store it back on people[i]
}

A subtle bug in copying with extend

The Computed Property doesn't work because the way angular.extend copies references, people[i].fullName is copied to (new Person()).fullName, which means that the (new Person()).fullName is calculating from the previous people[i].fullName, because it uses the 'self' reference.

(let me know if I need to draw a picture)

There are two ways to fix this:

1. We can fix how we extend existing records.

//...
for (var i=0; i < l; i++){
  people[i] = angular.extend( people[i] || new Person(), jsonPeople[i] );
  // OR  people[i] and new Person()
  // so that if there is an existing Person object, it is kept
}

2. We can fix how we define the Person class. I think this is the better method.

function Person(){
  var self = this;
  
  self.firstName = "";
  self.lastName = "";
  
  Person.prototype.fullName = function(){
    // re-connect 'self' to the current object
    var self = this;
    return [self.firstName,self.lastName].join(" ");
  };
}

This bumps the fullName method to the prototype/supertype, so it is no longer an immediate property defined on the Person object.

Summary

Notes on doing computed property in AngularJS
How to define a Class for AngularJS
How to handle extend and extend an array
How to move computed methods to the prototype
Plunker http://plnkr.co/edit/HcuxnT3EAVrtz1PyWwXb check out the two Count1 and Count2 computed properties and how they work differently after you clicked 'update'

July 21, 2015

Notes on KnockoutJS Mapping and ViewModel style guide

July 21, 2015/ John Liu

I wanted to write down some of the better practices I've settled with since using KnockoutJS for nearly two years now. A lot of these has to do with just avoiding errors that I see later on, as well as working with the peculiarities of the Knockout Mapping library.

These are not definitive, so let me know if you REALLY disagree!

function PersonViewModel(data) {
  var self = this;
  
  self.firstName = ko.observable();
  self.lastName = ko.observable();
    
  ko.mapping.fromJS(data, {}, self);

  self.name = ko.computed(function(){
    return ko.unwrap(self.firstName) + " " + ko.unwrap(self.lastName);
  });
}

Class Definition

Define a class, I always name the class CapitalizedCase, as opposed to camelCase for variables. Makes it clear when I'm about to instantiate a variable
I also always name ViewModel separately from just normal classes. ViewModel are special, they are for data-binding. To me, PersonViewModel is different from Person.

You can now create a view model like this.

var personVM = new PersonViewModel();

You can also define a class this way

var PersonViewModel = function(data){
  var self = this;
  
  // ...
};

But if you do it this way, understand that Javascript Hoisting is now in effect, and the class is not available until this line.
Also, remember the trailing semi-colon if you go for this assign variable syntax.

Property Definition & Knockout Mapping

ko.mapping.fromJS can be used to instantiate properties as a constructor. But there are potential issues. Consider:

function PersonViewModel(data) {
  var self = this;
  
  //self.firstName = ko.observable();
  //self.lastName = ko.observable();
  //if we don't define these...
    
  ko.mapping.fromJS(data, {}, self);

  self.name = ko.computed(function(){
    return ko.unwrap(self.firstName) + " " + ko.unwrap(self.lastName);
  });
}

var johnVM = new PersonViewModel( { firstName: "John", lastName: "Liu" });
var marcVM = new PersonViewModel( { firstName: "Marc" });

In marcVM, self.lastName is not created by ko.mapping and does not exist, and some binding statements will fail
So always declare (annoying) all the observable properties that you need. Don't trust some REST response to always return data that you need.

Knockout Mapping Definition

I go with this style for defining Knockout Mapping definitions.

function PersonViewModel(data) {
  var self = this;
  self.firstName = ko.observable();
  //...
}
PersonViewModel.mapping = {
  create: function(options){
    return new PersonViewModel(options.data);
  },
  key: function(data) {
    return ko.unwrap(data.firstName);
  }
};

The reason is that as you'll see in next example, you need the mapping from time to time, might as well keep it in one place that you can access easily.
I have also seen people put mapping on ViewModel.prototype.mapping - the benefit I see with this is that within the class, you can refer to it via self.mapping (but I think that lacks clarity).

You can now do this:

var data = {firstName:"John"};
var person = ko.mapping.fromJS(data, PersonViewModel.mapping);

This gets more fun when you have nested Observable Arrays of Objects

function PeopleViewModel(data) {
  var self = this;
  self.teachers = ko.mapping.fromJS([], PersonViewModel.mapping);
  self.students = ko.mapping.fromJS([], PersonViewModel.mapping);
  
  ko.mapping.fromJS(data, {}, self);
}
PeopleViewModel.mapping = {
  create: function(options){
    return new PeopleViewModel(options.data);
  },
  teachers: PersonViewModel.mapping,
  students: PersonViewModel.mapping
  // Reuse the mapping defined above!
};

var data = { 
  teachers: [
    { firstName: "John" },
    { firstName: "Marc" }
  ],
  students: {
    { firstName: "Bob"}
  }
};
var peopleVM = new PeopleViewModel(data);
var index = peopleVM.teachers.mappedIndexOf({firstName:"Marc"});

// index == 1

Summary

Some notes on structuring your ViewModel classes for readability, avoiding binding issues and Knockout Mapping gotchas.

You can try the example in this Plunker

John Liu .NET

John Liu .NET

Blog

John Liu .NET

AngularJS - Logging Client Side Stack Trace

Logging the Exception

stacktraceJS

Tweaks

Future of stacktraceJS

Expect the syntax to change, soon.

AngularJS $http and logger Circular Dependency

Error

Story

Error!

Final Code Summary

PhantomJS and Office 365 Brisbane

AngularJS Extend and Computed Property

KnockoutJS Computed Property

AngularJS binds Native Javascript Object

Defining Class for AngularJS

AngularJS Extend

Extending Arrays

A subtle bug in copying with extend

Summary

Notes on KnockoutJS Mapping and ViewModel style guide

Class Definition

Property Definition & Knockout Mapping

Knockout Mapping Definition

Summary

John Liu .NET

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