Communicating with java from typescript

Question

I wrote java program that takes one argument and writes it. Also, it reads lines and writes them. Then, I compiled it and ran from Typescript (vscode extension).

    const { spawn } = require('node:child_process');
    const runJava = spawn('java', ['-cp', 'extension1/src', 'package.Main', 'aaa']);

    runJava.stdout.on('data', (data: String) => {
        console.log(`stdout: ${data}`);
    });

    runJava.stderr.on('data', (data: String) => {
        console.error(`stderr: ${data}`);
    });

    runJava.on('close', (code: Number) => {
        console.log(`child process exited with code ${code}`);
    });

It writes 'aaa' to stdout successfully. What do I need to do next to send some text to it?

I tried to write with echo, but that didn't work.