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PREP FOR NEXT SESSION: https://github.com/HackYourFuture-CPH/JavaScript/blob/main/javascript3/week3/preparation.md

Promises

— Key concepts

• Why do we use Promises?

  • Because they allow us to handle asynchronous operations in JavaScript

• When do we use Promises?

  • When code would be blocking other code from executing while it is waiting for something, it is usually wrapped in a Promise to avoid that blocking behavior

• Resources & exercises

Promise Chaining

— Key concepts

• Follow these rules and you’ll be fine 🤪

  • Always end your chain with a catch
  • Never go deeper than 1 level
  • Always return a Promise from then, even if it’s just return Promise.resolve()

• Handy tips

  • Use Promise.all([...]) if you’re waiting for multiple ones
  • Use .catch(console.log.bind(console)) as a safe default, until you come up with a better way to catch your errors
  • Start your Promise chain with a new, empty Promise (no pun intended 😉) to make it more readable:

  Promise.resolve() .then(() => { // Your async operation ... return asyncOperation() }) .catch(console.log.bind(console))

• Why all these rules? Debugging issues in Promise chains can be very frustrating and these tips will help you avoid most pitfalls

• Resources & exercises

async / await

— Key concepts

• A different syntax for dealing with Promises and async code

• It lets us treat asynchronous code like it was synchronous code

• No freaky rules, you can start using it now

• Handy tips

  • Use try-catch whenever possible to make your code more stable
  • The async keyword is required in front of the closest function to wherever you use the await keyword
  • Functions with the async keyword return a Promise and need to be awaited (however, if you don’t care about the result, you can also omit it and let the function “run in the background”)
  • You can make all code into a Promise by wrapping it with new Promise()

• Resources & exercises