12^th Practical Class:
Asynchronous BE and how to log on server

Asynchronous JavaScript

• We're already using it!

But what is async/await? Let's look first at promises and basics quickly.

• JS runs code line by line and synchronously
• Long task might block the main thread!!! See this great example by MDN
• We need asynchronous code! Promises!
  • Code runs out of the main thread, notifies it when fulfilled or rejected using event loop
  • JS continuously checks for events in a queue, if they are resolved JS take them from queue and return them

Let's put it in our resolvers example:

• We can return a new Promise in callback function and chain promises to keep order in asynchronous calls.
• And catch all errors from all promises called before calling .
• But with chaining Promises, it can get messy pretty fast!

Use async/await instead

• Handling promises like a synchronous code using keyword
• Functions with has to be marked with keyword
• Can't be used on top level unless you're working with modules
• Code inside the function always wait until the Promise called after is fulfilled or rejected

Common mistake when returning data from async function and handling errors:

Our quack resolver using try/catch/finally

How to properly log on GraphQL server?

s are not enough, why?

• No structure
• Every developer can log differently, are you using dots at the end of sentence?
• Missing metadata -> unless you manually add them to every log
• Problem with where to log things

Use tools or your implementation of log

• Start with using logger tool
• Uses api under the hood, but provides better structure and options
• Usually has main logging methods (levels): , , ,
  • Each represent different severity
  • Displaying each can be configured based on deployment based on levels -> show only and on PROD
• There are many logging tools, we'll be using Pino
• You can also write your own tool, an abstraction over api

How to log in ApolloServer

• Logs should be traceable
  • To request, user, and mutated data
• Logs should be as automatic as can
  • Lifecycle/event logging
• Pass your logger via context, or use ApolloServer logger prop

Apollo Plugins

• Provides a way to work with GraphQL lifecycle
• You write a plugin method that are hooked to server lifecycle events or request lifecycle events
• All plugins and event handling functions have access to the context and request itself

Let's see the implementation in Quacker