Why does the following code not change the property in my object in Node.js

Question

Why does the following code not change the property in my object in Node.js

Suppose I setup test2.js as follows

module.exports.doPrint = doPrint;

var dummy = "initial";

function doPrint(callback) {
    setInterval(function() {
        console.log(dummy);
        callback();
    }, 1000);   
}

I then have test1.js

var test2 = require("./test2");
test2.doPrint(function() {
    console.log("changing");
    test2.dummy = "new value";
});

When I run test1.js I get the following

initial
changing
initial
changing

In other words the value of dummy in test2.js never gets changed to the new value. Can someone explain what is happening here?

javascript
node.js

Answer 1

It does not change the value because dummy is a local variable (can't be accessed from outside - variables local to the module will be private). To make it work you can change test2.js to this:

module.exports.doPrint = doPrint;

function doPrint(callback) {
    var that=this;
    this.dummy = "initial";
    setInterval(function() {
        console.log(that.dummy);
        callback();
    }, 1000);   
}

or use:

module.exports.doPrint = doPrint;
module.exports.get = get;
module.exports.set = set;

var dummy = "initial";

function get(){
    return dummy
}

function set(new_value){
    dummy=new_value;
}


function doPrint(callback) {
    setInterval(function() {
        console.log(dummy);
        callback();
    }, 1000);   
}

and test2.set("new value"); to change the value, if you want it to be a local variable.