getting-started-with-node-js.md

title	Getting Started with Node JS
group	software-languages
author	@liam-b

{% include /style/icon.html type="warning" %} Note that Node JS run really slowly on the EV3 brick and is limited to NPM version 0.10.29 which can be a problem when trying to install some libraries. {: .alert .alert-warning}

Before you start, make sure that you have configured a network connection to your ev3dev device and have opened an SSH connection to it.

Installing ev3dev-lang

To install the library run:

npm install ev3dev-lang

Now whenever you want to use this in code, just write:

var ev3dev = require('ev3dev-lang');

For a bit more info on this visit the ev3dev-lang github page.

Nano

For this tutorial, we will be using nano. For more info on how to use nano check out the nano cheat sheet.

Hello world

Navigate to a project directory (e.g ~/src/js) and make a new file with touch test.js

Open it with nano test.js and write:

var test = 'hello world!';
console.log(test);

Running node test.jsshould print hello world! to the console. If this worked you are ready to start coding with node!

Motors

Plug a ev3 large motor into port A, then open test.js and write:

{% include /style/icon.html type="warning" %} This snippet of code will not work for any other motors! {: .alert .alert-warning}

var ev3dev = require('ev3dev-lang');

var motor = new ev3dev.LargeMotor('outA'); // create new motor plugged into port A called 'motor'

motor.runForever(200); // run motor at speed 200

setTimeout(function () {
  motor.stop(); // stop the motor after a second
}, 1000)

If you get any errors when you try to run this, make sure your motor is plugged in correctly.

For other motors such as the MeduimMotor, check the default supported motors list.

And from reading the documentation page you should be able to get a good idea of what methods you can use with the motor (things like runForever() and runForTime()). Then when you use it in code, it should look like:

motor.doSomething(speed, otherArgument) // where doSomething can be replaced by any valid method.

You can also reset and read the position of a motor using motor.reset() and motor.position.

Sensors

Plug a ev3 color sensor into port 1, then edit test.js again appending this to the bottom:

var sensor = new ev3dev.ColorSensor('in1'); // create new color sensor called 'sensor'. in1 refers to port 1

setInterval(function () {
  console.log(sensor.reflectedLightIntensity); // log the reflected light percent of the sensor every 300 milliseconds
}, 300)

For other sensors, check the default supported sensors list.

To change a sensors mode you'll need to check what modes it has by looking at the ev3dev sensor list and use:

sensor.mode = 'NEW-MODE'; // where 'NEW-MODE' can be replaced by any valid mode

And then using sensor.someValueAcessor will return the sensor value, where someValueAcessor can be replaced by any valid accessor (also found on the default supported sensors list by clicking on the sensor you are using)

Next steps

So that's the basic overview of how to use node with ev3dev! For info on all supported sensors, motors and other documentation visit the github page and the documentation page.

The documentation page looks a bit confusing, but what you really need to worry about are the names of the classes and the methods / accessors. (eg. the large motor has methods such as: runForever(), runForTime() etc and the color sensor has accessors such as: reflectedLightIntensity, ambientLightIntensity etc)

The sensor list and the motor list are both really useful pages aswell.