Use GraphQL subscription to show progress of time-consuming operations

GraphQL is feature-rich query language designed to fit majority of needs of generic online applications. The 3 main types of operations in GraphQL are query, mutation and subscription. While queries and mutations are send in HTTP requests, subscriptions are running on WebSocket, which enables it to receive updates in real time. In this article, I would like to talk about using the subscription to report real-time results and/or progresses to time-consuming operations.