When calling end() on a pool connection, the function does not execute the provided callback. In the promise API, the promise does not resolve.

The type definitions indicate that this should be the expected behaviour:

• Callback API
  

  node-mysql2/typings/mysql/lib/Connection.d.ts

  Line 384 in d950b98

  end(callback?: (err: QueryError | null) => void): void;

• Promise API
  

  node-mysql2/promise.d.ts

  Line 63 in d950b98

  end(options?: any): Promise<void>;

The implementation of end() for the pool connection does not have any parameters so cannot execute any provided callback. The promise API doesn't call resolve() on the wrapping Promise:

• Pool connection end
  

  node-mysql2/lib/base/pool_connection.js

  Line 32 in d950b98

  end() {

• Pool connection end promise wrapper
  

  node-mysql2/lib/promise/connection.js

  Lines 63 to 67 in d950b98

  	end() {
  	return new this.Promise((resolve) => {
  	this.connection.end(resolve);
  	});
  	}

The fix for this should be to align the implementation with the type definitions - support providing a callback and resolving the promise for pool connections. I'd be happy to submit a PR for this if this feels like the right approach.