examples: https://github.com/alanbacon/typescript_examples

Intro

Thank for coming to this presentation on typescript. I guess the overarching goal here is to try and share some tips and tricks for removing the any types from our code base. The any type prevents intelliSense from helping us the developers know what methods and variables are available on our objects and can therefore be the source of many bugs.

Outcomes

There are a few main outcomes I would like from the session:

• For everyone to understand how to use type predicates, this helps turn our unknown types in known ones.
• To see how the relatively new satisfies operator is used, and why its useful
• Everyone to have an appreciation of discriminated unions

Type Predicates

• One of the main places any is left in the meta-backend code base is in the catching of errors, we could be using a mixture of unknown and type predicates to remove them.
  • Then we could turn on the stricter typescript checking to forbid implicit and explicit any from the code base.
• Using the as keyword can be pretty dangerous as you lose type-checking because you are telling the compiler you know better.
  • It's fine and even necessary in some cases (like when you are deserialising a JSON response)

Satisfies

• Another good way to remove the as keyword form the code base.
• Its great for locking down objects to something you know can be serialisable.
• A type level Satisifies type can be created really easily.
• There are some other used cases for satisfies as well. But ill let you watch the video on that in your own time.

Generics Foundations

I now want to talk about discriminated unions: But to make sure we're on the same page ill start with some foundations

• intro to type variables/parameters
• how to build more complex types using type variables
• the three ways to use the extends keyword
• the in keyword
• look ahead to discriminated unions

Discriminated Unions

• more advanced but great when you want to write some generic code for types that are similar but varied