JSFiddle - React, Tailwind, and code Playground

JavaScript

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

var str = 'foo.bar.baz.rar';

// solution
var parts = str.split('.');
var tmp;

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