Better way to cast object to primitive

Let's create class like:

var Klass = function() {}
Klass.prototype {
  string: functioin() { /* return as string */ },
  number: functioin() { /* return as number */ },
  boolean: functioin() { /* return as string */ }
};

This code use like:

var obj = new Klass();
obj[typeof any]() == any; // Yet another type casting

Enjoy!