code: function dropIndex(coll, indexName, options, callback) {
    // Delete index command
    const cmd = { dropIndexes: coll.s.name, index: indexName };
  
    // Decorate command with writeConcern if supported
    applyWriteConcern(cmd, { db: coll.s.db, collection: coll }, options);
  
    // Execute command
    executeCommand(coll.s.db, cmd, options, (err, result) => {
      if (typeof callback !== 'function') return;
      if (err) return handleCallback(callback, err, null);
      handleCallback(callback, null, result);
    });
  }
docs: Drop an index from this collection.
  
  @method
  @param {Collection} a Collection instance.
  @param {string} indexName Name of the index to drop.
  @param {object} [options] Optional settings. See Collection.prototype.dropIndex for a list of options.
  @param {Collection~resultCallback} [callback] The command result callback