How to make private varaible in JS

Question

I want to save a private variable(secret) when require a file/module. The secret shall be saved in the "object" of file sec_test.js and it shall not be readable or writable just execution-able. Is this a correct way?

Question 1: Is it possible to get the secret somehow during execution from the testing_sec_test.js?

Question 2: is it possible to have a constructor-ish function in sec_test.js ?

file: sec_test.js

module.exports = function (string) {
    var module = {};
    let secret = null;


    module.get_secret_length = function (callback) {
        generate_secret();
        if(secret == null){
            const json_err = {
                "Success":false,
                "error":"generating secret failed"
            };
            callback(json_err,null);
        }else{
            const json_err = {
                "Success":true,
                "result":"secret has been generated",
                "secret_length":get_secret_length()
            };
            callback(json_err,null);
        }
    }

    function generate_secret(){
        if(secret == null){
            secret = getRandomString()+string+getRandomString(); 
        } 
    }

    function get_secret_length(){
        return secret.length; 
   }

    function getRandomString(){
        const length = Math.floor(Math.random() * Math.floor(200));
        const characters_allowed = '@1#2$3&/=?:.;,+_-><~*^|4567890'+
        'qwertyuioplkjhgfdsazxcvbnmQWERTYUIOPLKJHGFDSAZXCVBNM';
        let random_string = "";
        for(let i =0;i<length;i++){
            let random_nbr = Math.floor(Math.random() * Math.floor(characters_allowed.length));
            random_string += characters_allowed.charAt(random_nbr);
        }
        return random_string;
    }


    return module;
};

file: testing_sec_test.js

const sec_test = require('./sec_test')("IS THIS SECRET A PRIVATE VARIABLE");

console.log(sec_test.get_secret_length.toString());

sec_test.get_secret_length(function(err,result){
    if(err){
        console.log(err);
    }else{
        console.log(result);
    }
});

---------------------------------------------------------------

---

I Guess i have to formulate my question a little better,, sorry

Question 1: Is it possible to get the key or ivKey AFTER the object has been required and the parameter has been inputed. Or is this object not safe to use becase its key or ivKey is public accessable?

---

file: testing_sec_test.js

//lets pretend that these keys is written in from the terminal to the object and are NOT hardcoded in the code!.
let sec_Obj = {
    "key": '1234zr3p67VC61jmV54rIYu1545x4TlY',
    "ivKey": "123460iP0h6vJoEa",
    "salt": "1kg8kfjfd2js93zg7sdg485sd74g63d2",
    "key_iterations": 87923   
  }

const sec_test = require('./sec_test')(sec_Obj);
sec_Obj = null;

console.log(sec_test);
let plain_text = "This is a national secret";
console.log("plain_text == "+plain_text);
sec_test.encrypt(plain_text,function(err,encrypted){
    if(err){
        console.log(err);
    }else{
        console.log("encrypted == "+encrypted);
        sec_test.decrypt(encrypted,function(err,decrypted){
            if(err){
                console.log(err);
            }else{
                console.log("decrypted == "+decrypted);
            }
        });      

    }
});

---

file: sec_test.js

const crypto = require('crypto');
module.exports = function (keysObj) {
    //is the parameter keysObj private?? 
    var module = {};

    module.encrypt = function (clearData,callback) {
        let str_encoding = "utf8";
        let encoding = "base64";
        try {
            let encipher = crypto.createCipheriv('aes-256-ctr', getPrivateKey(), getPrivateIvKey());
            let result = encipher.update(clearData, str_encoding, encoding);
            result += encipher.final(encoding);
            callback(null,result);
        } catch (error) {
            callback({"success":false,"error":error},null);
        }   
    }

    module.decrypt = function(encrypted,callback) {
        let str_encoding = "utf8";
        let encoding = "base64";
        try {
            let decipher = crypto.createDecipheriv('aes-256-ctr',getPrivateKey(), getPrivateIvKey());
            let result = decipher.update(encrypted, encoding, str_encoding);
            result += decipher.final(str_encoding);       
            callback(null,result);
        } catch (error) {
            callback({"success":false,"error":error},null);            
        }
    }

    //is this a private function
    function getPrivateKey(){
        return crypto.pbkdf2Sync(keysObj['key'], keysObj['salt'], keysObj['key_iterations'], 32, 'sha512');
    }

    //is this a private function
    function getPrivateIvKey(){
        return new Buffer(keysObj['ivKey']);
    }

    return module;
};

Answer 1

Simple example

var privateVar = 'private';


module.exports = {

   test:function(){
       console.log('I am '+privateVar);
    }
}

var test = require('./test.js');

//logs i am private
test.test()
//logs undefined
test.privateVar