Quick start - creating your first application

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by Gabriel Manricks | August 2013 | Open Source Web Development

In this article created by Gabriel Manricks, the author of Instant Meteor JavaScript Framework Starter, we will learn how to create your first application using Meteor Javascript Framework.

(For more resources related to this topic, see here.)

By now you should have Meteor installed and ready to create your first app, but jumping in blindly would be more confusing than not. So let’s take a moment to discuss the anatomy of a Meteor application.

We have already talked about how Meteor moves all the workload from the server to the browser, and we have seen firsthand the folder of plugins, which we can incorporate into our apps, so what have we missed? Well MVVM of course.

MVVM stands for Model, View, and View-Model. These are the three components that make up a Meteor application. If you’ve ever studied programming academically, then you’ll know there’s a concept called separation of concerns. What this means is that you separate code with different intentions into different components. This allows you to keep things neat, but more importantly—if done right—it allows for better testing and customization down the line. A proper separation is one that allows you to remove a piece of code and replace it with another without disrupting the rest of your app.

An example of this could be a simple function. If you print out debug messages to a file throughout your app, it would be a terrible practice to manually write this code out each time. A much better solution would be to “separate” this code out into its own function, and only reference it throughout your app. This way, down the line if you decide you want debug messages to be e-mailed instead of written to a file, you only need to change the one function and your app will continue to work without even knowing about the change. So we know separation is important but I haven’t clarified what MVVM is yet. To get a better idea let’s take a look at what kind of code should go in each component.

  • Model: The Model is the section of your code that has to do with the backend code. This usually refers to your database, but it’s not exclusive to just that. In Meteor, you can generally consider the database to be your application’s model.
  • View: The View is exactly what it sounds like, it’s your application’s view. It’s the HTML that you send to the browser. You want to keep these files as logic-less as possible, this will allow for better separation. It will assure that all your logic code is in one place, and it will help with testing and code re-use.
  • View-Model: Now the View-Model is where all the magic happens. The View-Model has two jobs—one is to interface the model to the view and the second is to handle all the events. Basically, all your logic code will be going here.

This is just a brief explanation on the MVVM pattern, but like most things I think an example is in order to better illustrate.

Let’s pretend we have a site where people can share pictures, such as a typical social network would. On the Model side, you will have a database which contains all the user’s pictures. Now this is very nice but it’s private info and no user should be able to access it. That’s where the View-Model comes in. The View-Model accesses the main Model, and creates a custom version for the View. So, for instance, it creates a new dataset that only contains pictures from the user’s friends. That is the View-Model’s first job, to create datasets for the View with info from the Model. Next, the View accesses the View-Model and gets the information it needs to display the page; in our example this could be an array of pictures.

Now the page is built and both the Model and View are done with their jobs. The last step is to handle page events, for example, the user clicks a button. If you remember, the views are logic-less, so when someone clicks a button, the event is sent back to the View-Model to be processed.

If you’re still a bit fuzzy on the concept it should become clearer when we create our first application.

Now that we have gone through the concepts we are ready to build our first application. To get started, open a terminal window and create a new folder for your Meteor applications:

mkdir ~/meteorApps

This creates a new directory in our home folder—which is represented by the tilde (~) symbol—called meteorApps. Next let’s enter this folder by typing:

cd ~/meteorApps

The cd (change directory) command will move the terminal to the location specified, which in our case is the meteorApps folder. The last step is to actually create a Meteor application and this is done by typing:

meteor create firstApp

You should be greeted with a message telling you how to run your app but we are going to hold of on that, for now just enter the directory by typing:

cd firstApp
ls

The cd command, you should already be familiar with what it does, and the ls function just lists the files in the current directory. If you didn’t play around with the skel folder from the last section, then you should have three files in your app’s folder—an HTML file, a JavaScript file, and a CSS file. The HTML and CSS files are the View in the MVVM pattern, while the JavaScript file is the View-Model.

It’s a little difficult to begin explaining everything because we have a sort of chicken and egg paradox where we can’t explain one without the other. But let’s begin with the View as it’s the simpler of the two, and then we will move backwards to the View-Model.

The View

If you open the HTML file, you should see a couple of lines, mostly standard HTML, but there are a few commands from Meteor’s default templating language—Handlebars. This is not Meteor specific, as Handlebars is a templating language based on the popular mustache library, so you may already be familiar with it, even without knowing Meteor. But just in case, I’ll quickly run through the file:

<head>
<title>firstApp</title>
</head>

This first part is completely standard HTML; it’s just a pair of head tags, with the page’s title being set inside. Next we have the body tag:

<body>
{{> hello}}
</body>

The outer body tags are standard HTML, but inside there is a Handlebars function. Handlebars allows you to define template partials, which are basically pieces of HTML that are given a name. That way you are able to add the piece wherever you want, even multiple times on the same page. In this example, Meteor has made a call to Handlebars to insert the template called hello inside the body tags. It’s a fairly easy syntax to learn; you just open two curly braces then you put a greater-than sign followed by the name of the template, finally closing it o ff with a pair of closing braces. The rest of the file is the definition of the hello template partial:

<template name=”hello”>

<h1>Hello World!</h1>
{{greeting}}
<input type=”button” value=”Click” />
</template>

Again it’s mostly standard HTML, just an H1 title and a button. The only special part is the greeting line in the middle, which is another Handlebars function to insert data. This is how the MVVM pattern works, I said earlier that you want to keep the view as simple as possible, so if you have to calculate anything you do it in the View-Model and then load the results to the View. You do this by leaving a reference; in our code the reference is to greeting , which means you place whatever greeting equals to here. It’s a placeholder for a variable, and if you guessed that the variable greeting will be in the View-Model, then you are 100 percent correct.

Another thing to notice is the fact that we do have a button on the page, but you won’t find any event handlers here. That’s because, like I mentioned earlier, the events are handled in the View-Model as well.

So it seems like we are done here, and the next logical step is to take a peek at the View-Model. If you remember, the View-Model is the .js file, so close this out and open the firstApp.js file.

The JS file

There is slightly more code here, but if you’re comfortable with JavaScript, then everything should feel right at home.

At first glance you can see that the page is split up into two if statements— Meteor.isClient and Meteor.isServer. This is because the JS file is parsed on both the server and the user’s browser. These statements are used to write code for one and not the other. For now we aren’t going to be dealing with the server, so you don’t have to worry about the bottom section.

The top section, on the other hand, has our HTML file’s data. While we were in the View, we saw a call to a template partial named hello and then inside it we referenced a placeholder called greeting . The way to set these placeholders is by referencing the global Template variable, and to set the value by following this pattern:

Template.template_name.placeholder_name

So in our example it would be:

Template.hello.greeting

And if you take a look at the first thing inside the isClient variable’s if statement, you will find exactly this. Here, it is set to a function, which returns a simple string. You can set it directly to a string, but then it’s not dynamic. Usually the only reason you are defining a View-Model variable is because it’s something that has to be computed via a function, so that’s why they did it like that. But there are cases where you may just want to reference a simple string, and that’s fine.

To recap, so far in the View we have a reference to a piece of data named greeting inside a template partial called hello, which we are setting in the View-Model to the string Welcome to firstApp.

The last part of the JS file is the part that handles events on the page; it does this by passing an event-map to a template’s events function.

This follows the same notation as the previous, so you type:

Template.template_name.events( events_map );

I’ll paste the example’s code here, for further illustration:

Template.hello.events({
‘click input’ : function () {

// template data, if any, is available in ‘this’
if (typeof console !== ‘undefined’)
console.log(“You pressed the button”);
}
});

Inside each events object, you place the action and target as the key, and you set a function as the value. The actions are standard JavaScript actions, so you have things such as click, dblclick, keydown, and so on. Targets use standard CSS notation, which is periods for classes, hash symbols for IDs, and just the tag name for HTML tags. Whenever the event happens (for example, the input is clicked) the attached function will be called.

To view the full gist of event types, you can take a look at the full list here: http://docs.meteor.com/#template_events

It would be a lot shorter if there wasn’t a comment or an if statement to make sure the console is defined. But basically the function will just output the words You pressed the button to the console every time you pressed the button. Pretty intuitive!

So we went through the files, all that’s left to do is actually test them. To do this, go back to the terminal, and make sure you’re in the firstApps folder. This can be achieved by using ls again to make sure the three files are there, and by using cd ~/meteorApps/firstApp if you are not looking in the right folder. Next, just type meteor and hit Enter, which will cause Meteor to compile everything together and run the built-in web server. If this is done right, you should see a message saying something like:

Running on: http: // localhost:3000/

Navigate your browser to the location specified (http : //localhost:3000), and you should see the app that we just created. If your browser has a console, you can open it up and click the button. Doing so will display the message You pressed the button, similar to the one we saw in the JS file.

I hope it all makes sense now, but to drive the point home, we will make a few adjustments of our own. In the terminal window, press Ctrl + C to close the Meteor server, then open up the HTML file.

A quick revision

After the call to the hello template inside the body tags, add a call to another template named quickStart. Here is the new body section along with the completed quickStart template:

<body>
{{> hello}}
{{> quickStart}}
</body>
<template name=”quickStart”>
<h3>Click Counter</h3>
The Button has been pressed {{numClick}} time(s)
<input type=”button” id=”counter” value=”CLICK ME!!!” />
</template>

Summary

I wanted to keep it as similar to the other template as possible, not to throw too much at you all at once. It simply contains a title enclosed in the header tags followed by a string of text with a placeholder named numClick and a button with an id value of counter. There’s nothing radically different over the other template, so you should be fairly comfortable with it.

Now save this and open the JS file. What we are adding to the page is a counter that will display the number of times the button was pressed. We do this by telling Meteor that the placeholder relies on a specific piece of data; Meteor will then track this data and every time it gets changed, the page will be automatically updated. The easiest way to set this up is by using Meteor’s Session object.

Session is a key-value store object, which allows you to store and retrieve data inside Meteor. You set data using the set method, passing in a name (key) and value; you can then retrieve that stored info by calling the get method, passing in the same key.

Besides the Session object bit, everything else is the same. So just add the following part right after the hello template’s events call, and make sure it’s inside the isClient variable’s if statement:

Template.quickStart.numClick = function(){
var pcount = Session.get(“pressed_count”);
return (pcount) ? pcount : 0;
}

This function gets the current number of clicks—stored with a key of pressed_count —and returns it, defaulting to zero if the value was never set. Since we are using the pressed_count property inside the placeholder’s function, Meteor will automatically update this part of the HTML whenever pressed_count changes.

Last but not least we have to add the event-map; put the following code snippet right after the previous code:

Template.quickStart.events({
‘click #counter’ : function(){
var pcount = Session.get(“pressed_count”);
pcount = (pcount) ? pcount + 1 : 1;
Session.set(“pressed_count”, pcount); }
});

Here we have a click event for our button with the counter ID, and the attached function just get’s the current count and increments it by one. To try it out, just save this file, and in the terminal window while still in the project’s directory, type meteor to restart the web server.

Try clicking the button a few times, and if all went well the text should be updated with an incrementing value.

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Instant Meteor JavaScript Framework Starter [Instant] Enjoy creating a multi-page site, using the exciting new Meteor framework! with this book and ebook
Published: April 2013
eBook Price: $12.99
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About the Author :


Gabriel Manricks

Gabriel Manricks is a full stack software & web developer focusing on PHP and both frontend and server-side JavaScript frameworks.

Gabriel works as a staff writer for NetTuts+, where he enjoys learning as well as teaching others, and he also freelances in web consulting, development, and writing.

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