meteor/minimongo/selector_modifier.js
function (obj, keys) {
  return _.all(obj, function (v, k) {
    return _.contains(keys, k);
  });
}
function (obj, keys) {
  return _.all(obj, function (v, k) {
    return _.contains(keys, k);
  });
}
function ( obj , keys ) { return _ . all ( obj , function ( v , k ) { return _ . contains ( keys , k ) ; } ) ; }
A helper to ensure object has only certain keys
A helper to ensure object has only certain keys