Cannot call class as a function Javascript

Question

I am building a simple stream to publish on PubNub and later consume. I can successfully utilize separate functions which log the output to the console or even create a .json file using the .pipe(new function()). However for some reason with this function I am getting the Cannot call a class function. I have not changed the syntax of the function call at the end of the code, so I am assuming it is something in the PubNubStreamOut() function itself.

TypeError: Cannot call a class as a function at _classCallCheck (D:\pasco\node_modules\pubnub\lib\node\index.js:27:99) at _class (D:\pasco\node_modules\pubnub\lib\node\index.js:37:5) at new PubNubOutStream (D:\pasco\pubnub.js:24:13) at Object. (D:\pasco\pubnub.js:54:42) at Module._compile (module.js:635:30) at Object.Module._extensions..js (module.js:646:10) at Module.load (module.js:554:32) at tryModuleLoad (module.js:497:12) at Function.Module._load (module.js:489:3) at Function.Module.runMain (module.js:676:10)

The .js file follows:

var pubnub = require('pubnub');
var util = require('util');
var Readable = require('stream').Readable;
var Writable = require('stream').Writable;
var Twitter = require('twitter');

var pncfg = {
   ssl           : true,  //  enable TLS Tunneling over TCP
   publish_key   : "PUB_KEY",
   subscribe_key : "SUB_KEY"
};

var twcfg = {
    consumer_key:"...",
    consumer_secret:"...",
    access_token_key:"...",
    access_token_secret:"..."
}



function PubNubOutStream(cfg, channel) {
   Writable.call(this,{objectMode:true});
   var pn = pubnub(cfg);

   this._write = function(obj, encoding, callback) {
       pn.publish({
           channel: channel,
           message: obj,
           callback: () => callback()
       });
   };
}
util.inherits(PubNubOutStream, Writable);

function TwitterStream(cfg, query) {
    Readable.call(this,{objectMode:true});

    var client = new Twitter(cfg);

    this._read = function() { /* do nothing */ };
    var self = this;
    function connect() {
        client.stream('statuses/filter', {track: query},
            function(stream) {
               stream.on('data', (tweet) => self.push(tweet));
               stream.on('error', (error) => connect());
            });
    }
    connect();
 }
 util.inherits(TwitterStream, Readable);

new TwitterStream(twcfg,"#twitter").pipe(new PubNubOutStream(pncfg,"awesome-tweets"));

I am not sure why I am getting the class as a function error since I am using the new PubNubOutStream()

Have you tried defining PubNubOutStream as a class instead of as a function? developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/… — Kevin Boucher
– Kevin Boucher, Commented May 29, 2018 at 19:35
I think the problem may be Writable.call(this,{objectMode:true}); — Barmar
– Barmar, Commented May 29, 2018 at 20:20

Alex Demidoff · Accepted Answer · 2018-05-29 20:44:20Z

1

According to PubNub's documentation, you should use the following syntax to create a new instance:

var PubNub = require('pubnub');
var pn = new PubNub({
    publishKey : 'demo',
    subscribeKey : 'demo'
});

The error is due to the fact, that you are calling the PubNub constructor as a function:

var pn = pubnub(cfg);

And the error message just confirms that:

TypeError: Cannot call a class as a function at _classCallCheck

Hope this will put you back on track.

answered May 29, 2018 at 20:44

Alex Demidoff

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