I would assume an error in your config results in a broken template, which typically gives the “undefined” on your mirror, because the nunjucks template could not be loaded.
Can you post your config of the module?

@k-0
I like the module idea very much. Could help some people around here.

So your problem is handling the asynchrous call? Is that right?
I think, the node_helper function is ideal to help with this (at least for a beginner).
What I would do, as someone who has his own problems with asynchronous calls:

start function:

    start: function() {
        Log.info("Starting module: " + this.name);
        // Set locale.
        this.sendSocketNotification("CONFIG", this.config);
        var self = this;
        setInterval(() => {
          self.updateDom();
        }, self.config.updateInterval);
    },

in node_helper.js:

socketNotificationReceived: function(notification, payload) {
    if (notification === 'CONFIG') {
        this.config = payload;
        this.collectData();
        self = this;
        setInterval(function () {
            self.collectData();
        },  10 * 60 * 1000);
    }
  },

  collectData: function () {
    request(url, function (error, response, body) {
      .....
      self.sendSocketNotification("DATA", response);
    });
  }

});

You basically have two separate intervals: The “async call” interval in node_helper and the dom update interval in your main js.
After the first asynchronous call you have always some data to show in the dom update interval. This data gets overwritten whenever node_helper sends a socketNotification.

Have a look at my rather short module using an asynchronous call:
https://github.com/lavolp3/MMM-Celebrations

If you upload your module on github we can have a better look at the code and make suggestions.

Hope it helps.

@sdetweil Sam, sorry to say that after such a long time I’m still not through with this.
Promises make my head explode, so I hope you can help me.

    scheduleUpdates: function() {
      var self = this;

      setInterval(function() {
        var conf = self.config;
        self.updateDom(conf.animationSpeed);

        setTimeout(function() {
          self.createBarChart();
        }, 2000);
      }, this.config.updateInterval);
    },

This is an easified version of my loop to update the dom.
You can see the timeout function I have built in to wait 2 seconds and be sure the dom has been created. Then in the createBarChart function I can write the chart into the dom.
This works, but I don’t like it at all.
Isn’t there a way to “await” the resolved promise from outside of the updateDom function? After all updateDom() returns a promise.
I have tried to do self.updateDom().then( function() {self.createBarChart() });
It didn’t work.

Thanks for your support. Really appreciated.

@BD0G
The css way is not as easy as I would have assumed.

All the elements in the forecast belong have “.forecast-item .hourly” classes so are not distinguishable.
I currently don’t know of a pure css way to get in between them and give the first daily forecast a margin or a border.

@mrdenmark thinking about that again the better way would be to give the daily forecast part a border-top in your custom css. That way you would not have to struggle when you want to update the module.
Let me know if you need help with that.

@mrdenmark well, you COULD go into the .njk template file and put in an <hr /> just above this part

        {# Daily #}
        {% if config.showDailyForecast %}

or give the forecast-item hourly classes a border-top: 1px solid #cccvia css.

OK, I’ll go for one:

#	username	width (m)	height (m)	real area (m²)	area to pay for (min. 0,4 m²)	location of delivery	additional comments (like polished edges)
1	Ivanov_d	0,8	0,73	0,58	0,58	Bulgaria	polished edges
2	fribse	0,7	0,6	0,42	0,42	Denmark	polished edges
3	lavolp3	0,666	0,666	0,44	0,44	Germany (NRW)

@Lordy Ich weiß nicht recht.
Meine config sieht so aus:

    {
        //disabled: true,
        module: 'MMM-Celebrations',
        position: 'top_left',
        header: "HEUTE IST:",
        config: {

        }
    },

Probiere die doch mal aus.

@dcarls91 I’m not sure if what you did was right.

For me the best way and proven a hundred times is:

• sit at an external device (laptop/PC)
• SSH into the mirror
• npm start dev
• open the mirror’s page on a browser on the laptop/PC (http://IP.OF.THE.MIRROR:8080)
• check the shell console (where you did the npm start dev) as well as the developer’s console of the browser for errors.

There will be something that will help you find the error

@sdetweil
good point! Then to be safe
cd .. && npm install electron@3.0.13