TypeScript

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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​
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function Render(props: {uri?: string}) {
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function toJSON(
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  value: any,
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  { pretty }: { pretty: boolean }
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) {
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  const indent = pretty ? 4 : 0;
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  return JSON.stringify(value, null, indent);
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}
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Objects
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interface LRUHashMap  {
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  [value: number]: DoublyLinkedList;
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}
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​
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class LRUHash {
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  private hash: LRUHashMap;
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​
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  construct() {
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    this.hash = {};
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  }
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}
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Enums cannot be keys
This fails:
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const enum Key { ... }
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const config: { [key: Key]: string } = {};
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Keys can only be string or number.
Use Map instead:
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const enum Key { ... }
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const config = new Map<Key, string>();
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React
​https://github.com/sw-yx/react-typescript-cheatsheet​
children
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interface Props {
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  children?: any;
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}
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Recommended https://github.com/Microsoft/TypeScript/issues/6471#issuecomment-171456118​
useRef
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export default function UriField() {
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  const [uri, setURI] = useState<string | null>(null);
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  const inputRef = useRef<HTMLInputElement>(null);
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  const onClick = () => {
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    if (!inputRef ||
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        !inputRef.current) {
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      return;
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    }
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​
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    setURI(inputRef.current.value);
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  }
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​
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  return (
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    <>
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      <input ref={inputRef} type="text" />
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      <input onClick={onClick} type="submit" value="Submit"/>
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    </>
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  );
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}
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Koa
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Last modified 3yr ago
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Contents
Versioning
Compiler Options
Sharing between models
Typing
Objects
React