How do you call a recursive method from within a method in javascript with nodejs?

Question

I am trying to setup a connection to my MySQL database and so far it is working, but when i run the nodejs application, and i don't read/update anything in my database the connection shuts down with:

Error: Connection lost The server closed the connection

So i searched on google and found this stackoverflow question. But i cannot get it to work, and i think it is because i am working with a class and not a function.

Below is the code i currently have:

class ConnectionFactory {

    constructor() {
        this.connectAndHandleDisconnect();
    }

    connectAndHandleDisconnect() {
        connection = mysql.createConnection(db_config);

        connection.connect(function(err) {
            if(err) {
                console.log('error when connecting to db:', err);
                setTimeout(connectAndHandleDisconnect, 2000);
            }
        });

        connection.on('error', function(err) {
            console.log('db error', err);
            if(err.code === 'PROTOCOL_CONNECTION_LOST') {
                connectAndHandleDisconnect();              // Error pops up from this line
            } else {
                throw err;
            }
        });
    }
}

And i am getting the following error message:

ReferenceError: connectAndHandleDisconnect is not defined

I have tried to replace the connectAndHandleDisconnect() to this.connectAndHandleDisconnect() and self.connectAndHandleDisconnect() but i have no clue how to find the fix to this error.

Odds are it didn't work when you used this because you used this inside of function(err), but the problem is this in that scope refers to function(err), not to ConnectionFactory, so (function(err){/* ...*/}).connectAndHandleDisconnect doesn't exist. You need to bind this outside of the function body. Similarly, the self approach wouldn't work if you did not bind self outside the function body. — gabriel.hayes
– gabriel.hayes, Commented Jan 21, 2020 at 18:02
The reason it works in the example you gave in your question is because they have declared handleDisconnect in the global scope, you haven't declared it in the global scope, so it needs to be qualified based on its scope as an instance member. — gabriel.hayes
– gabriel.hayes, Commented Jan 21, 2020 at 18:04

gabriel.hayes · Accepted Answer · 2020-01-21 17:58:51Z

You need to access methods via this (or with a reference to the instance that has the method) like so:

class ConnectionFactory {

    constructor() {
        this.connectAndHandleDisconnect();
    }

    connectAndHandleDisconnect() {
        connection = mysql.createConnection(db_config);
        const self = this;
        connection.connect(function(err) {
            if(err) {
                console.log('error when connecting to db:', err);
                setTimeout(self.connectAndHandleDisconnect, 2000);
            }
        });

        connection.on('error', function(err) {
            console.log('db error', err);
            if(err.code === 'PROTOCOL_CONNECTION_LOST') {
                self.connectAndHandleDisconnect();              // Error pops up from this line
            } else {
                throw err;
            }
        });
    }
}

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