checking 'deep' namespaces for existence and type

is.js

(function(host) {
    host.is = function is(namespace, type) {
        var ret = true,
            parent = host,
            chunks = namespace.split('.');
            
        chunks.forEach(function(e, i) {
            if ( parent === null ) { //this has to be straight equality check, can't lookup properties on null
                ret = false
                return //break
            }
            if ( typeof parent[e] != 'undefined' || (i == chunks.length-1 && type == 'undefined') ) {
                parent = parent[e]
            }
            else {
                ret = false
                return //break
            }
        });
        
        if (type) {
            typeof parent == type || (ret = false);
        }
        
        return ret;
    };
})(this);

Example:

var Foo = {
  bar: {
    start: function() {
      alert(this.flag)
    },
    flag: false
  }
}

console.log(
    is('Foo'),                          //is Foo defined
    is('Foo.bar'),                      //is Foo.bar defined
    is('Foo.bar.start', 'function'),    //is Foo.bar.start defined and of type 'function'
    is('Foo.bar.flag'),                 //is Foo.bar.flag defined
    is('Foo.bar.flag', 'boolean'),      //is Foo.bar.flag defined and of type 'boolean'
    is('Foo.bar.stop'),                 //is Foo.bar.stop defined
    is('Foo.bar.stop', 'undefined')     //is Foo.bar.stop undefined
)

//=> true true true true true false true