Advanced Typescript for people in hurry

Bartosz Szewczyk

>6 @ Codete

2022

Me, my bike and my dress code

Game that I'm making in my free time

(not released yet)

Overview

1. Type Guards
2. Strict Mode
3. Enums
4. Advanced types tips
5. Breaking Typescript
6. Useful links & materials

Typescript has become more powerful

What can you build with types alone?

How about a sorting algorithm?

1. Type guards

How to determine a specific type

Type guards #1

An interface with optional values

Solution #1

Solution #2

Type guards #2

A type union

Solution #1

Solution #2

Type guards #3

An unknown type

When do we encounter unknown

Solution

Type guards #4

Discriminated union types

Bonus feature

for discriminated unions
since 4.6

2. Strict mode

2. Strict mode

1. strictNullChecks
2. strictBindCallApply
3. strictFunctionTypes
4. strictPropertyInitialization
5. useUnknownInCatchVariables

2. Strict mode

1. strictNullChecks
2. strictBindCallApply
3. strictFunctionTypes
4. strictPropertyInitialization
5. useUnknownInCatchVariables

strict null checks

strict function type

no bivariant or contravariant shenanigans

strict function type

Incremental strict mode

How to apply it only to part of application 🤔

3. Enums in typescript

How can we create an enum in typescript

Enums

Can we mix them?

4. Advanced Types tips

• Type conditionals
• Mapped Types
• Infer Types

Type conditionals #1

Type conditionals #1

Type conditionals #2

Type conditionals #3

Type conditionals #4

IsEqual #1

Type conditionals #4

IsEqual #2

Type conditionals #4

IsEqual #3

Mapped types #1

Mapped types + conditional types

Mapped types on arrays

Mapped types on arrays #2

Infer Types #1

Infer Types #2

Infer Types #2

How to fix it?

Conditional + Mapped + Infer-Types

Solution

5. Breaking typescript

Example #1

Methods strict check

Example #1.1

Methods strict check

With createNameGetter

Example #2

Strict function type with void return

Example #3

TS depend on duck-typing just like JS

6. Useful links

Like what you saw?

Want to become a Typescript Pro?

Say no more!

Useful utilities libraries

1. SimplyTyped
2. utility-types
3. ts-toolbelt

type challenges

Exiting upcoming features

Instantiation Expressions

Before:

Instantiation Expressions

After TS 4.7

Thank you

Bartosz Szewczyk

👨🏼‍💻 Tech Lead @ Codete

@sztobar