RobotJS package gives users ability to control mouse and keyboard of the desktop. In our demo, we will try to draw a circle in MS Paint by controlling mouse actions. Here we will be using version 0.47 of RobotJS.

Development Environment:

1. JetBrains Webstorm
2. NPM 5.5.1

We will start by creating a simple node application in WebStorm.

Installing RobotJS:

Enter following command in terminal:

npm install robotjs --save

WebStorm creates a lot of boilerplate for us.

Next, we will set a route in our app.js as ‘draw’ where we will be adding our actions to draw different types of shapes.

...

...
var index = require('./routes/index');
var users = require('./routes/users');
var draw = require('./routes/draw');

...

...

app.use('/', index);
app.use('/users', users);
app.use('/draw', draw);

...

...
Code language: PHP (php)

Next, we will create ‘draw.js’ file in ‘routes’ directory of the project.

We will be using the polar form of the circle ie.:

x = R * cosθ

y = R * sinθ

for drawing the points of the circle by using angles ranging from 0-360.

Robot class provides following methods for keyboard and mouse events:

1. robot.keyTap(“tab”, “alt”) -> Performs a single keypress (first argument is a key and second argument is a modifier).
2. robot.getScreenSize() -> Returns the size of the desktop screen.
3. robot.setMouseDelay(0) -> Sets the delay in milliseconds to sleep after a mouse event.
4. robot.moveMouse(x, y) -> Moves mouse to x, y human like, with the mouse button up.
5. robot.mouseClick(“left”, false) -> Clicks the mouse (first argument is the mouse key and second argument is for double key press).

The draw.js class is as below:

var express = require('express');
    var robot = require("robotjs");

    var router = express.Router();

    router.get('/circle', function(req, res) {
    robot.keyTap("tab", "alt");

    var screenSize = robot.getScreenSize();
    var height = screenSize.height;
    var width = screenSize.width;

    var centerX = width / 2;
    var centerY = height / 2;

    var radius = Math.min(width, height) / 5;
    robot.setMouseDelay(0);

    for (var angle = 0; angle < 360; angle += 0.25) {
        var x = centerX + (radius * Math.cos(toDegrees(angle)));
        var y = centerY + (radius * Math.sin(toDegrees(angle)));

        robot.moveMouse(x, y);
        robot.mouseClick("left", false);
    }

    res.send('Bot at work');
});

function toDegrees (angle) {
    return angle * (180 / Math.PI);
}

module.exports = router;
Code language: JavaScript (javascript)

Final Drawing: