launch emulator and app only script for react native

launch-emu.js

#!/usr/bin/env node

// Most of the time when you launch the app you don't actually need to recompile the native app bundle. You only need to do that when you've added/removed/updated a native module. This allows running the emulator without compiling the app via `yarn emu`

const { execSync, spawn } = require("child_process");
const path = require("path");
const os = require("os");
const fs = require("fs");

const gradlePath = path.join(__dirname, "android", "app", "build.gradle");

const gradleContents = fs.readFileSync(gradlePath, "utf8");
const match = gradleContents.match(/applicationId\s+"(.+?)"/);

const applicationId = match ? match[1] : null;

if (!applicationId) {
    console.error("Could not determine application ID.");
    process.exit(1);
}

console.log(`Detected application ID: ${applicationId}`);

const androidHome = process.env.ANDROID_HOME || process.env.ANDROID_SDK_ROOT;
if (!androidHome) {
    console.error("ANDROID_HOME or ANDROID_SDK_ROOT is not set.");
    process.exit(1);
}

const emulatorPath = path.join(androidHome, "emulator", os.platform() === "win32" ? "emulator.exe" : "emulator");
const adbPath = path.join(androidHome, "platform-tools", os.platform() === "win32" ? "adb.exe" : "adb");

const runApp = () => {
    console.log("Launching the app...");
    const nullDevice = os.platform() === "win32" ? "NUL" : "/dev/null";
    execSync(`"${adbPath}" shell monkey -p ${applicationId} -c android.intent.category.LAUNCHER 1 > ${nullDevice} 2>&1`, { stdio: "ignore" });
}

try {
    const avds = execSync(`"${emulatorPath}" -list-avds`, { encoding: "utf8" })
        .trim()
        .split("\n");

    if (avds.length === 0) {
        console.error("No emulators found. Create one with `avdmanager`.");
        process.exit(1);
    }

    const emulatorName = avds[0]; // Default to first emulator
    console.log(`Starting emulator: ${emulatorName}`);

    // Check if an emulator is already running
    const devices = execSync(`"${adbPath}" devices`, { encoding: "utf8" })
        .split("\n")
        .slice(1)
        .filter(line => line.trim().endsWith("device"));

    if (devices.length > 0) {
        console.log("An emulator is already running. Skipping launch.");
        runApp();
    } else {
        const emulatorProcess = spawn(emulatorPath, ["-avd", emulatorName], {
            stdio: "inherit",
            detached: true
        });

        emulatorProcess.unref();

        console.log("Waiting for emulator to boot...");
        let loops = 0;
        const interval = setInterval(() => {
            try {
                const output = execSync(`"${adbPath}" shell getprop sys.boot_completed`, { encoding: "utf8", stdio: "pipe" }).trim();
                if (output === "1") {
                    clearInterval(interval);
                    console.log("Emulator is ready!");
                    runApp();
                }
                else if (loops < 15) {
                    loops++
                } else {
                    console.error("Gave up waiting for emulator");
                    clearInterval(interval);
                }
            } catch(error) {};
        }, 2000)
    }

} catch (error) {
    console.error("Error:", error.message);
    process.exit(1);
}

Make executable and add this to your package.json scripts

    "emu": "node launch-emu.js"