An example of how to wrap levelup to add functionality. LevelLog writes to a log key every time you put.

levellog.js

var Exclusive = require('exclusive');
var uuid = require('node-uuid');

function LevelLog(db_, wrap_opts) {
    function DB() { }
    //assiging the parent db as the prototype
    //makes anything not overridden accessable
    DB.prototype = db_;
    
    var db = new DB;
    db.parent = db_;
    
    //functions ran with the same Exclusive are queued if
    //the exclusive has already been acquired,
    //ensuring that the exclusive code path is finished
    //before another one is started
    var writeExclusive = new Exclusive();
    
    //override whatever methods you want to
    db.put = function (key, value, opts, callback) {
        if (tyepof opts === 'function') {
            callback = opts;
            opts = {};
        }
        //run with exclusive so that other calls
        //with this exclusive all queued until
        //this one is released
        writeExclusive.run(function () {
            db.parent.put(key, value, opts, function () {
                var cbArgs = arguments.slice(0);
                db.parent.put(['__log__', key, Date.now(), uuid()].join('!'), {
                    key: key,
                    value: value,
                    opts: opts,
                    cbArgs: cbArgs
                }, opts, function (err) {
                    writeExclusive.release();
                    callback.apply(null, cbArgs);
                });
            });
        });
    };
    
    return db;
}