JavaScript does not allow you to define a method as public or private. This is a limitation users need to get around to, because in real life you don’t want to expose all methods as public method.

Here is a simple implementation of the case where you want to verify input code.

 
function verifycode(code){
  console.log(code.length);
  return code.length == 4 ? true : false;
}

function info(code){
  if (verifycode(code)){
    console.log(code + ' is valid');
  } else {
    console.log(code + ' is wrong');
  }
}

info('abcd');
info('rty');

In the above implementation anyone can call the method verifycode. Not good. Here is one way to fix this problem.

 
var Lab = Lab || {};
Lab = (function() {
    var verifycode = function(code) {
        console.log(code.length);
        return code.length == 4 ? true: false;
    }
    return {
        info: function(code) {
            if (verifycode(code)) {
                console.log(code + ' is valid');
            } else {
                console.log(code + ' is wrong');
            }
        }
    }
})();

Lab.info('abcd');
Lab.info('rty');
Lab.verifycode('abcd'); //verifycode is private

Another way to solve the same problem would be to create a constructor function. Here is an implementation.

 
function Lab(code) {
        this.code = code;
    var verifycode = function() {
        return code.length == 4 ? true: false;
    };
    this.info = function() {
        if (verifycode()) {
            console.log(code + ' is valid');
        } else {
            console.log(code + ' is wrong');
        }
    }
}
(new Lab('abcd')).info();

Here is another way to solve the same problem. In this case I have moved all the public methods to prototype.

 
function Lab(code) {
    this.code = code;
    this.verifycode = function() {
        l = code.length;
        return l == 4 ? true: false;
    };
}

Lab.prototype.info = function() {
    if (this.verifycode()) {
        console.log(this.code + ' is valid');
    } else {
        console.log(this.code + ' is wrong');
    }
};

(new Lab('abcd')).info();