twitter out msg : error TypeError: Cannot read property 'length' of undefined

Louanne Dante

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Jul 18, 2016, 8:14:52 AM7/18/16

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Hello dear community,

i am about to write my bachelor-thesis about node-RED and i have quite an urgent issue.

I have a flow which should tweet the weather for the day when the flow is triggered, but the twitter out node says:

msg : error

TypeError: Cannot read property 'length' of undefined

The Flow requests weather data as a Javascript-Object from the yahoo weather API with a http-request node.

Then, in a function node I extract the weather data for today into a new msg1:

var forecast = msg.payload.query.results.channel.item.forecast;

var weather_today = vorhersage[0].text;

msg1 = {payload: weather_today, topic: "today"};

return msg1;

Next, I use a switch node that sends the message to different outputs, depending on the words that the payload contains.

For example, "when the payload contains 'Sun', send it to output 1, when it contains 'Rain', send it to output 2" and so on..

The different outputs of the switch node are connected to different function nodes, in which I generate different sentences, depending on the weather. These sentences should be tweetet later.

For example, when the msg.payload contains 'Sun', msg goes into the function node that generates sunny sentences like "Today its sunny in Berlin".

There are also function nodes that generate windy sentences and rainy sentences and so on.

I always want the tweets to be different. Thats why I increase (++) a global variable in a new function node after I generate the different tweet sentences. This happens everytime I trigger the flow ( button connected to the Raspi or simply via an Inject node).

Dependent on the number of the global variable I grab a different tweet out of the buffer everytime:

var tweet1 = "In Berlin it'll be sunny today.";

var tweet2 = "Today the sun is shining in Berlin.";

var tweet3 = "In Berlin the sun will shine today";

var tweet4 = "Today the sun is laughing in Berlin";

var tweet5 = "Berlin shows its sunny side today";

var tweetbuffer = [tweet1, tweet2, tweet3, tweet4, tweet5];

var change = context.global.flag;

msg.payload = tweetbuffer[change];

return msg;

I think that it is an easy error, but I dont know where to start. So I really would appreciate any help. Thank you!!

This is the flow for the clipboard:

Louanne Dante

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Jul 18, 2016, 9:06:02 AM7/18/16

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Sorry, forgot something:

The function node where i change the global variable looks like this:

if (context.global.flag == 4){

context.global.flag = 0;

return msg;

}else{

context.global.flag++

return msg;

}

Zenofmud

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Jul 18, 2016, 11:00:44 AM7/18/16

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backup your flow, then try changing that function to this

var f = global.get("flag");

if (f > 3){

f = 0;

} else {

f = f +1;

}

global.set("flag", f);

return msg;

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Louanne Dante

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Jul 18, 2016, 1:32:49 PM7/18/16

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Thanks for your quick response, Paul!

Unfortunately, your suggestion doesn't solve the problem.

But I just discovered, that after the function nodes where I generate the Tweet-Sentences, msg.payload turns out to be UNDEFINED.

So then it is no surprise that the twitter out node won't work.

But I wonder why it is undefinded, as I clearly say:

msg.payload = tweetbuffer[change];

return msg;

It works fine when I say:

msg.payload = "test";

return msg;

There must be an issue with the buffer, but I dont know how to figure it out.

Louanne Dante

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Jul 18, 2016, 2:33:02 PM7/18/16

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EDIT: Now i found out that there is an issue with catching the global variable... It is indicated as "null"....i will try further tomorrow

Louanne Dante

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Jul 18, 2016, 2:39:33 PM7/18/16

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Paul, sorry I first didn't understand your suggestion correctly at first. But now I think I do and there is an issue with catching the global variable. When I do it your way, the number is recognized as: NaN

Dave C-J

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Jul 18, 2016, 2:54:51 PM7/18/16

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The context.global.flag is never initialised in that function so the else can't then increment it. You need something like
context.global.flag =context.global.flag || 0;
To set it to 0 to start with if it's not already in existence.

Zenofmud

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Jul 18, 2016, 4:29:49 PM7/18/16

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Ahh yes, I when I was playing, I had an function to initialize it, sorry I forgot to mention that :>(

On Jul 18, 2016, at 2:39 PM, Louanne Dante <louann...@gmail.com> wrote:

Paul, sorry I first didn't understand your suggestion correctly at first. But now I think I do and there is an issue with catching the global variable. When I do it your way, the number is recognized as: NaN

Dave C-J

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Jul 18, 2016, 5:14:30 PM7/18/16

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Forgot to mention or forgot to re-apply it ? the symptoms you have are of it not being initialised.

Louanne Dante

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Jul 20, 2016, 6:29:14 AM7/20/16

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Thank you!!Unfortunately I have an exam on friday so I will try to figure it out after that:)

cflurin

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Jul 21, 2016, 5:00:19 AM7/21/16

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An alternative solution without global (sample for cloudy Tweets):

var msg1 = {};
var tweet;
var tweet_number = Math.floor(Math.random() * 4); // 0 .. 4

switch (tweet_number) {
case 0: tweet = "Berlin wird heute von Wolken verdeckt."; break;
case 1: tweet = "Heute wird es wolkig in Berlin."; break;
case 2: tweet = "Berlin ist heute voll von Wolken."; break;
case 3: tweet = "In Berlin ist es heute bedeckt."; break;
case 4: tweet = "Berlin ist heute wolkenbedeckt."; break;
default: tweet = "no tweet";
}

msg1.payload = tweet;
return msg1;

Louanne Dante

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Jul 27, 2016, 8:55:15 AM7/27/16

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thank you cflurin,

i got it working now with this:

1 var global = flow.get('save')||0;

2

3 if (global > 3){

4 flow.set('save','0');

5 msg.count= 0;

6 return msg;

7 } else{

8 global++;

9 flow.set('save', global);

10 }

11

12 msg.count = global;

13 return msg;

and then i caught the global variable in another function node with this:

1 var tweet0 = "Berlin wird heute von Wolken verdeckt.";

2 var tweet1 = "Heute wird es wolkig in Berlin.";

3 var tweet2 = "Berlin ist heute voll von Wolken.";

4 var tweet3 = "In Berlin ist es heute bedeckt.";

5 var tweet4 = "Berlin ist heute wolkenbedeckt.";

6 var add = " Die Höchsttemperatur liegt bei " + msg.temp +" °C.";

7 var tweetbuffer = [tweet0+add, tweet1+add, tweet2+add, tweet3+add, tweet4+add];

8

9 var zaehle = flow.get('save');

10 msg.payload = tweetbuffer[zaehle];

11 return msg;

Thank you all, this problem is solved

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