From JavaScript Patterns

var MYAPP = MYAPP || {};
 
MYAPP.namespace = function(ns_string) {
    var parts = ns_string.split('.'),
        parent = MYAPP,
        i;
 
    if (parts[0] === "MYAPP") {
        parts = parts.slice(1);
    }
 
    for (i = 0; i < parts.length; i += 1) {
        if (typeof parent[parts[i]] === "undefined") {
            parent[parts[i]] = {};
        }
        parent = parent[parts[i]];
    }
    return parent;
};
 
 
MYAPP.namespace("hello.world");
console.log(typeof MYAPP.hello.world); // object
console.log(typeof MYAPP.hello.something); // undefined