Question

I’m finding myself struggling with a little problem.
Let’s say I’ve got an object:

var foo = {
    bar: {
        baz: true
    }
};

Now I also have a String 'foo.bar.baz'. I’d now like to retrieve the value from the object using the string.

Please note: This is just an example, the solution needs to be dynamic.

Update:

I need the variable name also to be dynamic and parsed from the string. Also I can’t be sure that my variable is a property of the window.

I have already built a solution using eval, but this is pretty ugly I think:
http://jsfiddle.net/vvzyX/

Answer 1

Here is how you can do this:

function getValue(namespace, parent) {
    var parts = namespace.split('.'),
        current = parent || window;
    for (var i = 0; i < parts.length; i += 1) {
        if (current[parts[i]]) {
            current = current[parts[i]];
        } else {
          if (i >= parts.length - 1)
            return undefined;
        }
    }
    return current;
}
var foo = {
    bar: {
        baz: true
    }
};
console.log(getValue('foo.bar.baz')); //true

The first argument of the function is the namespace (dot separated values) and the second one is the parent object, if parent is not provided then window is used.

One more example using the parent argument:

var str = 'foo.bar.baz';
    foo = {
       bar: {
          baz: true
       }
    };

result = getValue(str, foo);
console.log(result);

Here is an example in jsfiddle.

Similar approach is used in YUI. Their approach is called Namespace pattern. The main benefit is simulation of packages/namespaces. The only difference between this script and the namespace pattern is that the namespace function creates nested structure instead of only returning value.