TypeScript

Pros:

• Useful for preventing me from pushing the quick hacks I'm trying to commit in JavaScript.

Cons:

• Modules you depend on may not have typescript definitions

  • To avoid typing, you may have to go backwards const ... = require()

• Definition hell

Versioning

Node	TypeScript Target	Support
6.17	es5	AWS Lambda Node v6.10 support
	es6
8.10-9.11.2	es2016
8.10-9.11.2	es2017	AWS Lambda Node v8.10 support
10-nightly	es2018	AWS Lambda Node v10.x support
	es2019

General Rules:

• If you are targeting for web set target to es5

• If you targeting for AWS Lambda, set your target to es2018

  • Node.js v10.x supports es2018

• If you are targeting for local and using the latest node, go for es2019

  • I'm assuming you can target for esnext as well as it wouldn't make sense to write code that the latest Node.js could write...but I could be wrong

Compiler Options

https://www.typescriptlang.org/docs/handbook/compiler-options.html

Enable:

• declaration: true when you want to share a Typescript code across modules

• jsx: react when you want to share a React component across modules

Sharing between models

Enable in your compiler option:

• declaration: true

• jsx: react

Typing

• https://www.sitepen.com/blog/typescript-cheat-sheet

function and object destructuring

https://mariusschulz.com/blog/typing-destructured-object-parameters-in-typescript

function Render(props: {uri?: string}) {

function toJSON(
  value: any,
  { pretty }: { pretty: boolean }
) {
  const indent = pretty ? 4 : 0;
  return JSON.stringify(value, null, indent);
}

Objects

interface LRUHashMap  {
  [value: number]: DoublyLinkedList;
}

class LRUHash {
  private hash: LRUHashMap;

  construct() {
    this.hash = {};
  }
}

Enums cannot be keys

This fails:

const enum Key { ... }
const config: { [key: Key]: string } = {};

Keys can only be string or number.

Use Map instead:

const enum Key { ... }
const config = new Map<Key, string>();

React

https://github.com/sw-yx/react-typescript-cheatsheet

children

interface Props {
  children?: any;
}

Recommended https://github.com/Microsoft/TypeScript/issues/6471#issuecomment-171456118

useRef

export default function UriField() {
  const [uri, setURI] = useState<string | null>(null);
  const inputRef = useRef<HTMLInputElement>(null);
  const onClick = () => {
    if (!inputRef ||
        !inputRef.current) {
      return;
    }

    setURI(inputRef.current.value);
  }

  return (
    <>
      <input ref={inputRef} type="text" />
      <input onClick={onClick} type="submit" value="Submit"/>
    </>
  );
}