lib/operations/collection_ops.js
function createIndex(coll, fieldOrSpec, options, callback) {
  createIndexDb(coll.s.db, coll.s.name, fieldOrSpec, options, callback);
}
function createIndex(coll, fieldOrSpec, options, callback) {
  createIndexDb(coll.s.db, coll.s.name, fieldOrSpec, options, callback);
}
function createIndex ( coll , fieldOrSpec , options , callback ) { createIndexDb ( coll . s . db , coll . s . name , fieldOrSpec , options , callback ) ; }
Create an index on the db and collection.

@method
@param {Collection} a Collection instance.
@param {(string|object)} fieldOrSpec Defines the index.
@param {object} [options] Optional settings. See Collection.prototype.createIndex for a list of options.
@param {Collection~resultCallback} [callback] The command result callback
Create an index on the db and collection .