Can a variable be made readonly in Node.js

Question

I want to prevent a variable from being changed. Specifically a property of an Object:

var foo = { bar: 'baz' };

// do something to foo to make it readonly

foo.bar = 'boing'; // should throw exception

Can this be done?

Answer 1

You could try

Object.defineProperty(foo, "bar", { writable: false });

and the later assignment either fails silently or, if you are in strict mode, throws an exception (according to David Flanagan's "JavaScript : The Definitive Guide" ).

Answer 2

Use a function:

var foo = function() {
  var bar = 'baz';

  return {
    getBar: function() {
      return bar;
    }
  }
}();

In that way foo.bar is undefined, you can only access it through foo.getBar();

Answer 3

Look at this example:

var Foo = function(){
     this.var1 = "A";   // public
     var var2 = "B";    // private
     this.getVar2 = function(){ return var2; }
}

var foo = new Foo();

console.log(foo.var1);   // will output A
console.log(foo.var2)    // undefined
console.log(foo.getVar2())    // will output B