AngularJS To do App – Part III

So continuing on and upwards, what every To do list should have, in no particular order are the following:

  • Check of an item
  • Edit an item
  • Delete an item

Incidentally the first thing that came to mind was the delete function (only when I had that did the rest occur, which arguably are more important features).

I somewhat implemented deleting by including a  button with a ngClick directive within the ngRepeat directive:

$scope.del = function() { $scope.items.pop(); }
<ul ng-repeat="items in items track by $index">
<li>{{ item }} <button type="submit" ng-click="del()">X</button></li>
</ul>

Sure, it should only affect the item it is (magically) tied to heh, heh… no. Pop didn’t go the weasel as it removes an array item from the end. And any other array method I’d come across didn’t seem to be able to remove items unless at the start or end. However, in that same post I had linked to ECMA-262 (Standards Document) which is the comprehensive language specification guide for ECMAScript, or JavaScript as its known as when not protecting Gotham city. That had fairly detailed (verbose) items about array methods – in particular Array.prototype.splice. I thought it was like slice but it seems similar to what a delete function should do:

Array.prototype.splice (start, deleteCount, ...items )
Note:  When the splice method is called with two or more arguments, start, 
deleteCount and zero or more items, the deleteCount elements of the array 
starting at integer index start are replaced by the arguments items. 
An Array object containing the deleted elements (if any) is returned.

Sounds about right, except I don’t want to want to replace anything with something else, nor return the deleted item. The language specification document is not the most user friendliest nor have any usable examples, but there’s tons of other information available on splice online.

W3schools.com states that the splice method adds AND removes items (holy utility belt stuffer Batman). Also it clearly states that second and third parameters are optional.

So our delete function is pretty similar to the add function:

$scope.del = function(index) { // parameter for index
  // start at index required and delete one item, which is itself
  $scope.items.splice(index, 1);
}

So in our HTML, we just need to just latch onto current index position of the item to which the delete button (with the ngClick directive which is iteratively assigned by ngRepeat) is attached.

Being the cool cat I am, I intuitively (counter it seems in hindsight) just threw in ‘this’ into the delete function as a parameter

...ng-click="del(this)">...

Because this is all powerful, this is better than that (except when you assign this to that). I should’ve known better than that – what I did was a total party foul, which I won’t get into at this moment. At that stage the list item was being removed from the top, like shift() would. The proper solution, it turns out, was staring at me all along.

I ran into the issue of not being able to create more than one item in the list, mentioned in the previous post, because AngularJS doesn’t like duplicates in the ngRepeat directive. The fix was add ‘track by $index’ – which assigns, and I quote, “each list item a key by virtue of its index…”

So now each added item has its own delete button which only applies to that item.

All the updates can be seen in the latest commit.
Updated functionality can be seen on the associated github page ‘ToDo’. (might need to do a hard refresh to get the latest working example).

More on the other features coming shortly…

ps I renamed my html file from ‘todo.html’ to ‘index.html’ which shows up in github diff as two different pages.

AngularJS To do App – Part II

When we last left, our intrepid developer in the making, he had had completed the shell and basic setup of his AngularJS app. Lets see what he’s upto this week…

The To do list has so far taken shape and the basic structure and logic was coded. However adding an item presented two issues:

  1.  We couldn’t add more than one item
  2.  The added item was bound to the new input field

Issue ‘1’ turned out to be Angular pointing out that the ngRepeat directive does not allow duplicates – the message could be seen in the console.

Angular error: Duplicates in repeater are not allowed.

This happens when there are duplicate keys in an ngRepeat expression. Also not having any key implies all items have the same key – food for thought. The resolution is adding  ‘track by $index’ to the ngRepeat attribute value

ng-repeat="item in item track by $index"

This assigns each list item a key by virtue of its index where there is no explicit key defined. This fixes issue ‘1’ and more items can be added to the model, however all of those added items are all bound together and in turn to the input box. So every time the value is updated, all instances are updated as well. [see commit]

After scouring the interwebs for a bit and running through a few related but not similar issues on stackoverflow and old old tutorials, I tried a few things

  • Changing the array of objects to just an array of strings [not much different but when you’re going crazy and it’s nearly bed time might as well]
  • Tried using different versions of angular [static library was used, an old version 1.2.16, then the latest and something in between]

Finally what worked was not passing in the new object created using the ngModel directive as a parameter in the ngClick directive on the button and then getting the object from the $scope directly within the add function call.

Before:

<input type=text ng-model=new.name/>
<button type=submit ng-click=add(new)>Add</button>$scope.add = function(item){
$scope.items.push(item);
…}

After:

<input type=text ng-model=new/>
<button type=submit ng-click=add()>Add</button>$scope.add = function(){
$scope.items.push($scope.new);
…}

Not entirely certain why it was fixed, but assuming that somehow accessing the object from the $scope ensures that each one is separate from the others and doesn’t end up being tied to the same instance as before.

For now it’s doing another aspect of what we intended to do – adding items to the list correctly without duplication.

I’ve pushed the changes [see commit] and added a github page to see it in action – To Do App

 

AngularJS To do App – Part I

So as outlined in my previous post AngularJS Single Page Application (SPA), I’ve started working on the bare bones (first commit) of the To do list app – so little that a Hello World tutorial would have had more moving parts [Zing].

I’ve started fleshing out the AngularJS aspects, particularly the module, controller and associated data holder (an array) and a function to add to that array (fingers crossed).

So far it’s not working. I pre-populated the array with an object literal containing a ‘Sample Item’ value in the hopes that it will render in the expression statement {{ }}. But nada. Some things I thought was the cause:

  • I’d placed all of the script tags at the bottom of the HTML page, so it would load only after the DOM was rendered. [moved it up]
  • I’d referred to the angular.js file in script tags and within those tags placed all the code. [moved the code to its own script tag]

So still trying to figure out why AngularJS isn’t initializing.

[UPDATE] Ok so turns out I missed the ngApp directive, woops¯\_(ツ)_/¯, which meant that it was just a plain old HTML file with odd little tags which mean nothing and displayed the double curlies as just content – {{ item.name }}.

With that done, I was able to get the array with the pre-populated object literal to appear and and… the ability to add a new item (One of the most main functions on a to do list). Unfortunately, the new input box is bound to the previously added item – it updates when you type in another item and can’t seem to add anything further.

Check out the code [ commit ] until now and stay tuned as I go scratch my head some.

AngularJS Single Page Application (SPA)

So for my next quest, I’ve decided to go with a Single Page Application for the following reasons:

  • To start exploring JavaScript frameworks
  • Get some much needed interactivity on screen
  • Increase the complexity of the projects I am going after to move out of my comfort zone

I’ve decided to test the water with AngularJS. Why you might be asking? Well the previous mini project I completed was using PHP, and to further build on that language I chanced upon a course on pluralsight Building a Site with AngularJS and PHP. Since tacit conditions mean I can’t write about non JavaScript related builds, it made sense to do a crossover. Granted, I doubt I will be using a PHP/AngularJS combo for what entails.

The pluralsight tutorial was interesting but the nature of tutorial videos and instructor bias of students understanding and assimilating information at the same level as they proffer the instructions, means that certain aspects would be glossed over with the student being none the wiser.

So, in keeping with the familiar thread throughout my journey, one of the best ways to learn is to attempt to build something yourself. And after much head scratching the best thing I could think of doing was a simple to do list. Yes partly because I have been drawing blanks and the fact of using something I have almost no clue about is daunting to say the least. Also this is a priming exercise to test the waters, so something overly complex isn’t the end goal.

So I shall start with the minimal of outlays and setups and progress from there as usual. Check out my ‘awesome’ concept sketch. Mind blowingly simple.

To do list concept sketch

Caveat: AngularJS is the first version that was released with Angular 2 onwards being a complete rewrite of the framework. So pursuing AngularJS is pure curiousity and what’s transferable to learning Angular2+ (currently Angular6 beta) might only be an exercise in comparative analysis.

What’s this? Second Anniversary for JavaScript: ‘Unscripted’

It seems the the world has gone around the sun completely once again. And this happens to be the two year mark for JavaScript: ‘Unscripted’.

A lot has happened since last year. The last few months were pretty hectic in more ways than one, which meant not a lot of work could be done on this blog. Just finished up a simple weather app today but since it was done in PHP (shh, not so loud) a write up didn’t happen here. See the app in action here weatherGetter [simple app, simpler name see git repo if you’re so inclined].

But all is not lost, it’s all part of the plane. One of which is to iterate on the design/functionality of this blog, which, surprise surprise, is built on PHP. Another facet of that is launching a sub-site which will focus on all matters which are not specifically JavaScript.

So here’s to another great year which will:

  • Push harder on the route to JavaScript mastery
  • Added focus on loftier goals such as design patterns, frameworks etcetera
  • More entries on learning styles, techniques and tips
  • More complex apps
  • And much more…

So stay tuned and have a great year.

 

Hoisting in JavaScript

Everyone’s heard the all too familiar, JavaScript is an interpreted language spiel. That’s only partly true. Certain instances  can catch unwary developers out about this idiosyncratic run-time behaviour.

When a JavaScript engine parses a code file, a global execution environment called the execution context is created. This occurs before the file is executed where functions, variables etcetera are ‘hoisted’ into memory. Think of this as instantiation in other languages.

Hoisting is what allows function calls, which occur before the function definition, to run without throwing an error – as the entire function will be hoisted to memory.

This causes issues where function expressions are used. Function expressions are anonymous functions which are assigned to a variable as opposed to a function statement:

// Function Statement
function doSomething(){
   console.log("something done");
}

// Calling 
functionHolder();

// Function Expression
var functionHolder = function() {
   console.log("doing something else");
}

In this case the variable functionHolder will be hoisted into memory, however it will be ‘undefined’ until the interpreter reaches the actual line where the anonymous function is assigned. At this instance a function object is created and assigned to the variable functionHolder.

For more details about functions expressions, see:
the official description on MDN
JavaScript functions
JavaScript callback functions

JSON and JavaScript Objects

JavaScript Object Notation (JSON) is the lightweight alternative to tag laden XML used as data exchange format. What it is, precisely, is a method of data transmission based on JavaScript’s object literal syntax.

JavaScript objects are containers which store key value pairs of attributes, functions and other objects of the following appearance:

var anObject = {
 firstProperty: 'someString',
 secondProperty: 111,
 aFunc: (parameter) {
         // some code
     };
 isJSON: false
}

JSON follows the same exact pattern:

{
  "firstProp": "someString",
  "secondProp": 222,
  "isJSON": true
}

Few items of note that distinguish between JSON and plain old JavaScript objects:

  • JSON requires that properties by enclosed in quotes, while JS Objects can do it either way.
  • JSON only contains key value pairs, no functions

Back and forth

Although not part of the language, its ubiquity means that JavaScript has helper methods to handle JSON. Most common function is to convert from an object literal to JSON and vice versa:

///////////////////////////////
// Object literal to JSON
///////////////////////////////
var myObject = {
   firstProp: "someString",
   secondProp: 222
}

var JSONresult = JSON.stringify(myObject); 
// Result
//  {"firstProp": "someString", "secondProp": 222 }

///////////////////////////////
// JSON to Object literal 
///////////////////////////////
JSON.parse(JSONResult);
// result
// { firstProp: "someString", secondProp: 222 }

So although similar, JS objects and JSON are not the same. In essence JS objects is how you might be normally at home, relaxed and casual versus while JSON is like being in public with more formalised rules.

HTML5 enhancements

Now it’s been some time since HTML5 came on the scene. It’s shiny new glean has been replaced with a well worn veneration and stability.

Although it’s made some marked improvements over its predecessors in terms of not requiring laboured attributes or overly strict syntax, one of its tenets means a certain level of backward compatibility still exists. And owing to the certain habits or strict requirements in the past, some developers simply would’ve stuck to those habits or not realised that with the latest iteration, that some items were no longer needed. This lists the obvious, and not so obvious items.

DOCTYPE

This is the most obvious one and one which is required. So, without delving into all the iterations and variances, the last two major branches, XHTML and HTML 4 series required a lengthy declaration of the schemas used for the document type defintion (DTD). HTML5 did away with all the cumbersome description and replaced it with the all too popular and well received

 <!DOCTYPE html>

Linking to external files

A CSS style sheet is referenced in an HTML file by using the <link> tag, while JavaScript is referenced via a src attribute in a <script> tag. Where the JavaScript reference required an attribute to specify it was of type ‘text/javascript’, and similarly with CSS being ‘text/css’, is no longer required.

<script src="js/script.js" type="text/javascript"></script>

Async

HTML5 enables asynchronous loading of scripts without locking the other processes from loading in a browser. This is done by using the async tag

<sript src="js/script.js" async></script>

How? By using the async attribute preventing users from having to worry about script link placement and all the consequences the decision imbues.

Defer

Defer is similar to the Async attribute, however, it can be used when multiple scripts are needed and should be loaded in order. Scripts with this attribute will wait to execute until the page has finished loading.

These are some of the enhancements for the moment. If there are ones that I have missed, especially major ones, let me know in the comments.

Get started using web API’s – Luas Forecasting API Part Three

After much struggles, see the previous entry for the history up til now, the responseText message was successfully parsed and the information populated on the page:

Luas Arrival Time

Luas Test App

Some of the pitfalls:

  • Response message was a string which wouldn’t yield to any XML extraction methods. That was sorted once parsed to XML. (Response methods for XML didn’t yield anything or issues further along made me dismiss it altogether.
  • It was impossible to extract any data, attempts yielded
    • XML Object Element.
    • HTML Object Element.
    • Null.
  • Xpath was used to get at the data but still no luck (some remnants can be seen as code or comments).
  • API was down for maintenance which didn’t allow much progress.

There were myriad of explanations and convoluted methods to get the data but the issue lay in that the information needed was in the attritbutes and not in the nodes. I’ll do a clearer, indepth write up of all the steps taken to create this but for now this shall be parked.

Some improvements I’m planning on however include:

  • Automatic updating of the page when the response refreshes.
  • Selecting stops by name and whether inbound or outbound.

Stay tuned for that and more!

Get started using web API’s – Luas Forecasting API Part Two

Continuing on from the last post – Get started using web API’s – Luas Forecasting API Part One , there was a slight issue I ran into. This was resolved after several commits where I’d tried to see if I could print out the response regardless of the response status. However those failed and can be seen in my commits [1] [2]

The issue was that I couldn’t get any response message back once the code was hosted on github pages – It worked perfectly on my machine (hey oh). It would just default to the else condition in the httpRequest’s onreadystatechange update – i.e. the assigned function alertContents() would return the message if the response wasn’t in a readyState of ‘DONE’ and status wasn’t 200.

else {
 alert('There was a problem with the request\n');
 alert(httpRequest.responseText); // added an alert to see what message 
                                  // being returned - there was none.

The responseText from the httpRequest didn’t contain any message to help troubleshoot. The problem was later pinned down to a mixed content issue – it’s one where the calling code requests a non secure request ‘http’ and the API would send back or expect a request call to be secure and hence return a secure response.

With that sorted, the next step still remains: Extract information from the xml response and update the webpage. For now here’s the page, click the button to get a raw response message in all its glory.