IMU.js

A lightweight JavaScript library for accessing and normalizing device motion and orientation sensors. IMU.js provides a simple interface to work with accelerometer, gyroscope, and device orientation data, with automatic handling of device orientation changes and sensor permissions.

Features

• 📱 Access device accelerometer and gyroscope data
• 🧭 Track device orientation changes
• 📐 Automatic sensor data normalization
• 🔄 Landscape/Portrait orientation detection and compensation
• 📊 Real-time motion magnitude calculations
• 🔒 Handles iOS sensor permissions
• ⚡ Lightweight with zero dependencies

Installation

CDN / Direct Download

Download the latest version: imu.umd.js

Include it in your HTML file:

<script src="imu.umd.js"></script>

NPM (Node.js / Webpack / Vite / Parcel)

Install via npm:

npm install imujs

Import in your JavaScript file:

import IMU from "imujs";

Quick Start

const imu = new IMU()

// Initialize on user interaction (required for iOS)
button.addEventListener('click', async () => {
    try {
        await imu.init()
        console.log("IMU initialized!")
        
        imu.listen(data => {
            console.log(data)
        })
    } catch (err) {
        console.error("IMU initialization failed:", err)
    }
})

API Reference

Constructor

const imu = new IMU()

Methods

init()

Initializes the IMU and requests necessary permissions. Returns a Promise.

await imu.init()

listen(callback)

Starts listening to sensor events. The callback receives sensor data.

imu.listen(data => {
    const { accel, rotation, orientation, screenOrientation, magnitudes } = data
})

removeListeners()

Stops listening to sensor events and cleans up event listeners.

imu.removeListeners()

Data Format

The callback receives an object with the following structure:

{
    accel: {
        x: "0.00",  // m/s², range: ±157 (±16g)
        y: "0.00",
        z: "0.00"
    },
    rotation: {
        x: "0.00",  // degrees/second, range: ±2000
        y: "0.00",
        z: "0.00"
    },
    orientation: {
        alpha: "0.00",  // compass direction (0-360)
        beta: "0.00",   // front/back tilt (-180 to 180)
        gamma: "0.00"   // left/right tilt (-90 to 90)
    },
    screenOrientation: {
        type: "portrait-primary",
        isLandscape: false,
        isPortrait: true,
        angle: 0
    },
    magnitudes: {
        accelMagnitude: "9.81",     // total acceleration magnitude
        rotationMagnitude: "0.00"   // total rotation magnitude
    }
}

Example Usage

Basic Motion Tracking

const imu = new IMU()

async function startTracking() {
    try {
        await imu.init()
        
        imu.listen(data => {
            const { x, y, z } = data.accel
            console.log(`Acceleration: X=${x}, Y=${y}, Z=${z}`)
        })
    } catch (err) {
        console.error("Failed to start tracking:", err)
    }
}

Orientation-Aware Game Input

const imu = new IMU()

async function setupGameControls() {
    try {
        await imu.init()
        
        imu.listen(data => {
            const { beta, gamma } = data.orientation
            const tiltForward = beta > 20
            const tiltSide = Math.abs(gamma) > 15
            
            if (tiltForward) movePlayerForward()
            if (tiltSide) movePlayerSideways(gamma)
        })
    } catch (err) {
        console.error("Failed to setup controls:", err)
    }
}

Motion Gesture Detection

const imu = new IMU()

async function detectShake() {
    try {
        await imu.init()
        
        let lastMagnitude = 0
        const SHAKE_THRESHOLD = 20
        
        imu.listen(data => {
            const { accelMagnitude } = data.magnitudes
            
            if (Math.abs(accelMagnitude - lastMagnitude) > SHAKE_THRESHOLD) {
                console.log("Shake detected!")
            }
            
            lastMagnitude = accelMagnitude
        })
    } catch (err) {
        console.error("Failed to setup shake detection:", err)
    }
}

Browser Support

• ✅ Chrome for Android
• ✅ Safari iOS (requires user interaction for permission)
• ✅ Chrome Desktop (limited sensor support)
• ✅ Firefox for Android
• ❌ Safari Desktop (no sensor support)

Notes

1. iOS requires a user interaction (like a button click) before requesting sensor permissions.
2. The device must support the required sensors.
3. Some browsers require HTTPS for accessing sensor data.
4. Screen orientation changes are automatically handled.

License

MIT License

Contributing

Contributions are welcome! Please feel free to submit a Pull Request.