TypeScript

Features

• better development-time tooling
• static code analysis
• compile-time type checking
• code level documentation

Main principle

Three parts

• language
• compiler (transpiler)
  • programmer can decide version of the generated code (EMCAScript 3 or newer)
  • removes the typing information
  • performs static code analysis
    • emit warnings/errors
    • perform tasks such as combining the generated code into a single file
• language service
  • collects type information from the source code and allow dev tools to provide intellisense

Diff with other typed languages

• type equivalence
• Others -> nominal type system - answer this question based on whether x is an instance of a class/type named {whatever type you're looking for}
  • require everything to be in classes
• TypeScript is a structural type system - only care about the shape of an object.
• wide to narrower

Basics

• [TypeScript Types]
• [Steps to Convert to TypeScript]

Interfaces vs Types

• type alias can handle primitives and is very flexible - string or number
  • sort eagerly
• interfaces limited to JS objects and sub types - arrays and functions
  • things that have prototype
  • can describe ojbect, functions, arrays
  • parse like functions - sorted out lazily

Express with Typescript

React with Typescript

• [Typed Action Creators and Reducer]
• [Use Function Component to Define Types]
• [useParams Hook Require Defined Type]

To Review

• function signature overloading
• lexical scope
• index signature - combining types and interfaces