What a week!

Over the last month or so I have been steadily learning Javascript, Bootstrap, NodeJS and AngularJS well last week added to that mix was D3JS. I must have got to the end of my tether every day last week. I’m pretty sure I was suffering from information overload and before going any further I will say D3JS is really powerful and looks to be a tool I’d like to learn to use, the only downside is even after a week of drawing circles, bar charts and trying line graphs I am still struggling, but hopefully my struggling has not been in vein I learn some good things and if I’d known them before I’d started a lot less pain and suffering would have ensued.

The problems

So I don’t know angular, I also really struggle to read large chunks of text like the APIs, I did do the tutorial which helps but not really… There were a number of issues, not knowing how angular worked interms of where the right place to put things was a big set back, not knowing how to get data between the various components and updated was another. Another area of challenge was the asynchronous nature of Angular, making a $http.get request and not having data available instantly is odd but easily over come once you know how.

In importance order…

Callbacks

A long while a go I wrote a blog called What University forgot to mention about programming, it turns out this was one of those things that would have been really useful to be learning if the course wasn’t dumbed down to cater for those that didn’t come from an IT background at college.

In short I was doing this:

var data = [];

function getData(){
  $http.get('/api/data').success(function(response) {
    data = response;
  });
}
getData();
alert("data is 0!? " + data.length);

The problem with this is that getData is called and initiates the $http.get which does not return data, it returns the promise of having data; When it actually gets a response it moves on to the function declared in then(). Remember the way Javascript works is we passed in that function as an Object which then gets run when the data returns, it passes in the response for us to then handle. Because $http.get returns a promise that function is done, everything executed, the anonymous function we declared is a parameter that has been forked in the browser or language somewhere and is running isolated from everything else.

The way around this is to structure code in a way that allows for the callback to then do what you needed so….

function getData(cb) {
  $http.get('/api/data').success(function(response){
    cb(response);
  })
}

function drawGraph(newData) {
  //some code to draw a graph omitted...
}

//Draw a graph
getData(drawGraph);

By using the above method you only draw the graph when there is data, take this; rinse and repeat and all will be well, except this method is only really good for a one time graph. Controllers only get called once, they can be used to set up functions to be used in the view etc but they are ultimately only run once.

Data Binding

Firstly, read about Data binding. This first mistake I made was trying to do everything in a controller, it’s the most natural as everything in there gets run like when you include a normal js file, but it just makes life harder than it needs to be.

Originally I was doing something like this:

function getData(cb) {
  $http.get('/api/data').success(function(response){
     cb(resp);
  });
}

function updateData(data){
  drawGraph(data);
}

function drawGraph(data){
  //some code to draw a graph omitted...
  getData(updateData);
}

//Draws initial graph and then kicks off an infinite loop of getting data/drawing graphs 
getData(drawGraph);

I was using this to update and draw a graph. This works sort of but I was not able to get it to work because of my understanding of D3Js at the time, I’m sure smarter people than I could make it work but that’s not how it should be done; theres a better way like explained in the link above about data binding.

If you take your partial (template) and put certain triggers in it, even manual like ng-click you can do this a lot simpler, you can even use $watch to continuously update. so if you were to define a function or two like this…

In your controller:

$scope.updateGraph = function() {
  getData(reDrawGraph);
}

function reDrawGraph() {
  //code to RE-DRAW not draw the graph
  //Enter new, Transition, exit... more later...
}

In your partial:

<button class="btn btn-success" ng-click="updateGraph()">

You can make it update as you go. One step further would be to use $scope.data and just have a loop in the controller that sets that when data comes back, combined with a $watch to always re-draw.

Directives

Okay, so directives are useful, Until I learnt about them I was drawing all of my graphs from the controller and by far the must successful graphs I did were all in the directives area. I still think there was a better way because I was struggling to get it to work with $watch either way by having this layer you achieve two things, less crap in the controllers, and a nice location to do the DOM manipulation, which for graph drawing is kind of handy. Because this links right in with the html it is easier to manipulate.

Summary

These are just some of the major hurdles I overcame while trying to get D3JS working, and there’s more to come when I get on to D3JS which I have to admit I only got basic graphs drawn but I do think it’s an area worthy of diving into with more detail. All in all these experiences have made my understanding of Angular a lot better I am now able to quickly and easily make changes to pages to do basic things like looping through JSON data to display lists of data or forms to submit data.

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