server variables in functions

Question

I have a function that gets called through a socket.io event. This function is in another moldule. I want to make sure that everytime the function gets called the variables in the module are not changed by previous function calls.

I know how to do this in other languages: create a new instance of an object, call the function but i cant seem to get this to work in javascript.

The code looks like this:

socket.io module where the functions gets called

// -- all events -- //
io.on('connection', function (socket) {
    console.log('user connected');

    socket.on('increase', function (data) {
        var increaser = require('./increase.js');
        increaser.increase();
    });
});

increase module, should print 1 everytime, but prints 1..2..3..4....

/*jslint node: true */
"use strict";

// -- variables -- //
var counter = 0;

module.exports = {
    increase : function () {
        counter += 1;
        console.log(counter);
    }
};

I want to know how to do this, because on my server a function gets called that calls a few asyncronous functions and i want to make sure that all variables stay like they are until the whole function is proccesed complete and dont get changed if another client connects and triggers the same event.

Aruna · Accepted Answer · 2016-11-13 22:33:22Z

1

You can do the same exactly like other languages using an instance of object as below.

Method 1: Simplest function object

/*jslint node: true */
"use strict";


module.exports = function() {
   this.counter = 0;
   this.increase = function () {
        this.counter += 1;
        console.log(this.counter);
   };
};

Method 2: Function with prototype

/*jslint node: true */
"use strict";

function Increaser() {

}

Increaser.prototype = {
   counter: 0,
   increase: function () {
        this.counter += 1;
        console.log(this.counter);
   };
};

module.exports = Increaser;

And at your socket.io,

// -- all events -- //
io.on('connection', function (socket) {
    console.log('user connected');

    socket.on('increase', function (data) {
        var Increaser = require('./increase.js');
        var increaser = new Increaser();
        //  Also you can use as below in one line
        // var increaser = new require('./increase.js')();
        increaser.increase();
    });
});

edited Nov 13, 2016 at 22:33

answered Nov 13, 2016 at 22:13

Aruna

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6 Comments

Jose Hermosilla Rodrigo Over a year ago

and now you can get rid of var counter = 0

Aruna Over a year ago

Yes right @JoseHermosillaRodrigo. corrected now :-)

Vujukas Over a year ago

@Aruna so i should export every variable the function uses with this.variable in the export function ?

Aruna Over a year ago

@Vujukas Yes, instead of a variable, you can use with this. Or you can use the same with prototype as I mentioned in method 2 above. Still you should use the property with this inside the increase method.

Vujukas Over a year ago

Thank you that really helped

|

Mike Monteith · Accepted Answer · 2016-11-13 22:14:19Z

0

The important concept here is that require() will always return the same object, not a new version each time.

So var increaser = require('./increase.js'); inside a callback is an anti-pattern. If you want a new object each time, consider making increase.js return a function which returns your increaser module. Then var counter will not be global.

answered Nov 13, 2016 at 22:14

Mike Monteith

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