console.log during an Underscore.js chain()

example.js

_.chain(myData)
  .flatten()
  .log()
  .reverse()
  .log()
  .filter(function(item) { return item.active; })
  .value();

underscorelog.js

_.mixin({
  log: function(arg) {
    console.log(arguments);
    return arg;
  }
});

Don't know why I didn't do this before. Very handy for quick debugging of intermediate chain states.