It's a little involved, but quite doable. You serialize objects using the asJSON expression, which basically turns an object into a string. You can then put all the JSON strings into an array, then JSON the array, which give you one long string that represents the entire level. You can put this big string into a text file, or upload it to a database somewhere for sharing.
To get your level back, get that string back form the text file or database, then create an array and setFromJSON. Then, for each item in the array, create an object and setFromJSON on that object, using the text from that point in the array. You may need a separate array to remember what type of object you need to create. Keep doing this and popping the strings out of the array until it is empty