Writing JavaScript for an Intel Edison
WARNING! This is a blog post in progress. I decided to publish it early so you can watch me work on it.
In my last article about the Intel Edison, I showed you how to take yours out of the box, and get it set up. Consider this article a follow-on. I'm going to pick up pretty much where the last one ended.
We actually wrote a little bit of code in the setup article, but in this one, we're going to learn...
- how to use the power of Node.js to bring in libraries and command our device
- how to deploy code to the device wirelessly
- how to use the excellent Cylon library to make our code elegant and expressive
Let's start off in this article without employing the help of Visual Studio, and then my next article will capture the many productivity benefits of VS. It's always nice to start at the base and climb up to awesome tooling. That way, we're thankful for the conveniences it brings. :)
Using Node.js
Installing Node.js
I'm assuming your host PC is Windows. I'm running the technical preview of Windows 10 and it's all working great. I like to live on the edge.
The easiest way to install Node.js is by simply clicking the big green button you'll find at nodejs.org...
You'll see in the installation wizard, that you're actually getting the NPM utility installed along with the Node.js engine. The installation should take care of a lot of busy work for you such as adding node and npm to your path so you can actually call it from the CLI. My CLI of choice, BTW, is PowerShell. To be clear, I'm talking here about installing Node.js on your host PC. Node should already be installed on the device if you flashed it according to the instructions in the last post.
After you have Node.js installed, we'll walk through a few steps to create a new node project on your host PC. When we're done with that, we'll turn our attention to getting that code over to the Edison and running it there.
Creating the Folder and File Structure
Node.js projects have a pretty well defined, convention based folder and file structure. They're very simple too - all of the metadata is in one spot. I don't know where you keep your development projects, but I keep all of mine under c:\repos and I'll start there. Watch the following video as I create a new project folder, generate an app package description file (package.json), and then create my initial app.js file...
As you can see, the npm init makes the creation of our package.json file very easy. The package.json file describes your node project and has a few purposes - the two most prominent that I can think of are a) it provides the metadata necessary in case we end up publishing this package to the node package store and b) it defines the project dependencies so that when the project is copied somewhere else, a simple command is all that's necessary to actually go out and copy in all binaries necessary for the app to work.
Writing the Code
Now, in keeping with a simple workflow at first, let's open app.js in Notepad++, and fill out the following...
var mraa = require('mraa'); var pin13 = new mraa.Gpio(13); pin13.dir(mraa.DIR_OUT); led.write(1);
This code depends on the mraa module, but if you followed my setup guide and flashed the Intel with the latest image, then you already have it. The mraa module
The code simply creates a new pin out of pin 13. Pin 13 is the one that conveniently has an LED on the dev board, so we don't even have to plug anything in to see it. It then sets the direction of that pin to out. And finally, it raises the logic level of the pin by writing a value of 1.
Executing Your New Code
We saw in the last guide how to SSH directly to our device. If you gave your device the name "eddie" like I did, then you've been provided a DNS name of eddie.local which represents the IP address that your device was assigned on the network. If you're not sure the device or the DNS name are working, just do ping eddie.local from the CLI (replacing 'eddie' with the name of your device of course).
First, we'll get our code copied to the device, and then we'll SSH to the device in order to execute the code. It is also possible to simply execute the node app.js command remotely with SSH, but it's fun to see what's actually happening.
In this video, I'm going to SSH to the device, make a directory for our hellonode app, then jump back to my host machine, copy the files to the device (and specifically to that project folder) using SCP, and then back to the device to execute the app. The workflow can be simplified a bit, but I'm not arguing at this point. It's pretty wonderful actually.
You didn't see anything happen there, but I did. My LED came on.
Now that's not bad, but I'm going to move on to the next step, which is using Visual Studio to make our entire experience all the better.
Using Visual Studio for Increased Developer Joy
Install Visual Studio Community