Joseph-Mutua / ts

The TS Type System

1. Helps catch errors during development
2. Uses 'type annotations' to analyze code
3. Only active during development
4. Doesn't provide any performance optimization

Syntax+Features vs Design Patterns with TS

• Syntax+Features: What is an interface? What is the syntax for defining an interface?:
  • Understand basic types in TS
  • Function typing + annotations
  • Type definition files
  • Arrays in TS
  • Module systems
  • Classes + Refresher on OOP
  • Projects
• Design Patterns with TS: How to use interfaces to write reusable code
  • Projects

Type- The different properties + functions that a value has:

• Used by the typescript compiler to analyze the code for errors
• Allow other engineers to understand the types in the codebase

TS Types

1. Primitive Types: number, string, boolean, symbol, void, null, undefined
2. Object Types: functions, classes, arrays, objects

• Type Annotations + Inference apply to variables, Functions, Objects
  • Type Annotations: Code added to tell TypeScript what type of value a variable will refer to
  • Type Inference: TS tries to figure out what type of value a variable refers to. If declaration and initialization are on the same line, TS will figure out the type annotation automatically.

When To Use:

Annotations

1. When we declare a variable on one line then initialize it later
2. When we want a variable to have a type that can't be inferred
3. When a function returns the "any" type and we need to clarify the value

Inference

Always!

Annotations around Functions

Type Annotations for functions: Code we add to tell TS what type of arguments a function will receive and what type of values it will return Type inference for functions: TS tries to figure out what type of value a function will return.

Array vs Tuple annotations

• Use typed Arrays any time you need to represent a collection of records with some a arbitrary sort order
• A Tuple s an Array-like structure where each element represents some property of a record

Interfaces: Creates a new type, describing the property names and values of an object.

• General Strategy for reusable code in TS
  • Create functions that accept arguments that are typed with interfaces
  • Objects/Classes can decide to 'implement' a given interface to work with a function

Class Modifiers

1. Public: This method can be called anywhere, anytime
2. Private This method can only be called by other methods in this class
3. Protected This method can be called by other methods in this class, or by other methods in child classes.