How do I know if a variable is private?

I've never understood private variables. I know how to make them, (using the Module Pattern, right) but I don't see what's so private about them. I illustrated an explanation on jsFiddle -- http://jsfiddle.net/fufWX/

Can you explain how that _private variable really is private when it is still accessible from the outerscope? And what are the use for private variables in the first place!? Thanks.

var Module = (function() {
    var _private = "My private variable";
    return {
        get: function() { return _private; },
        set: function(e) { _private = e; }
    };
})();
开发者_JS百科
var obj = {};


// How is that variable private when I can simply obtain it like this:
obj.get = Module.get; // ??
obj.set = Module.set; // ??

obj.get(); // "My private variable"

There's no such thing as a truly private variable in JavaScript. There are only local variables.

In your example, _private is "private" because, outside of the anonymous function, it is only accessible via the get and set functions your have provided. Without those functions, _private would be totally inaccessible outside of the anonymous function.

Further reading:

• Private Members in JavaScript
• OOP in JS, Part 1 : Public/Private Variables and Methods