Waiting for stream input from child process in Node.js

Question

My main Node.js process spawns a child process. I want to communicate to the child process by sending it data through its stdin and reading it out from its stdout. The child process will continue running. I want to send it a message, then wait for it to respond, do something with the response, and then continue the main process. How do I best do this? I tried the following:

    // I call this function after sending to child's stdin
    private async readWaitStream() {
        let data = '';

        let chunk = '';
        while (chunk = this._child.stdout.read()){
            data += chunk;
        }

        // doesn't finish because child process stays running
        await finished(this._child.stdout); 
        return data;
    }

The child process never finishes, and this doesn't work.

Answer 1

I figured out how to solve the problem. I use once.('readable' ... ), for example:

private readWaitStream() {
    return new Promise(resolve => {
        let data = '';
        this._child.once('readable', () => {
            let chunk = '';
            while (chunk = this._child.read()) {
                data += chunk;
            }
            resolve(data);
        });
    });
}

When I then the function, we will wait for input and the promise will only resolve after the next input is available.