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();