How can you find out what event a stdout message is coming from? NodeJS

Question

I'm currently working on a script where I want to be able to read the messages coming from child processes spawned from ShellJS NPM package, which uses NodeJS child_process. Currently, I am able to read most of the logs with the stdout.on("data", (data) => {...}) callback, But for some of the logs I need, they don't come through on the data event. I have tried a number of different event names, but nothing seems to pick them up. On the pic below, the messages I want but can't get through to my code are the ones with <i> at the beginning. These are all coming from webpack.

Anyone know how I could get these messages or find out what event they may be coming using?

This is my current code:

_setup(){
        this._shell = shell.exec("npm start", {
            async: true,
            cwd: this._app.cwd,
            silent: false
        })

        if(!this._shell.stdout){
            console.error("failed")
            return;
        }

        this._shell.stdout.on("data", (data) => this._onMessage(data))
    }

    _onMessage(data) {
        console.log("STDOUT message received", data)
        const found = data.match(/.*Loopback: http:\/\/localhost:(.*)\/.*/)

        console.log("found", found)

        this._onUpdate();
    }

Answer 1

So it appears that webpack logs come through on stderr as i got them coming through using:

this._shell.stderr.on("data", d => this._onMessage(d))