please give me first 20 Anki flashcards for below content:
```md
Very basic tsc usage
I guess I have to learn TypeScript now.
Here's how I got started in as few steps as possible, with the help of Get Started With Typescript in 2019 by Robert Cooper.
Installation using npm
I created a new project:
mkdir -p ~/Dropbox/Learning-TypeScript/first-typescript
cd ~/Dropbox/Learning-TypeScript/first-typescript
Then installed the TypeScript compiler:
npm install --save-dev typescript
Using --global instead of --save-dev would have installed in globally, but I'm not ready for that kind of commitment yet!
Apparently I need a tsconfig.json file. Running this command creates one for me containing some suggested defaults:
% ./node\_modules/.bin/tsc --init
Next step: create a .ts file to start testing it out. I put the following in greetings.ts:
const greeting = (person: string) => { console.log("Hello " + person); };
greeting("Simon");
Next, compile it! Thanks to npm install --save-dev typescript the tsc compiler is now available here:
% ./node\_modules/.bin/tsc
Run without any arguments it seeks out the tsconfig.json file, compiles any .ts files and produces matching .js files.
That seems to have worked:
% node greetings.js Good day Simon % cat greetings.js "use strict"; var greeting = function (person) { console.log("Good day " + person); }; greeting("Simon");
Running tsc --watch
The --watch command continues to run and automatically compiles files when they are saved:
% ./node\_modules/.bin/tsc --watch
[9:32:44 AM] Starting compilation in watch mode...
[9:32:44 AM] Found 0 errors. Watching for file changes.
I changed the last line of my greetings.ts file to greeting(1) (a type error) to see what happened:
[9:33:56 AM] File change detected. Starting incremental compilation...
greetings.ts:5:10 - error TS2345: Argument of type 'number' is not assignable to parameter of type 'string'. 5 greeting(1);
[9:33:56 AM] Found 1 error. Watching for file changes.
Using npx
Tip from @Benjie: you can use npx to avoid the ./node\_modules/.bin prefix.
I had thought that npx installed and ran a new global version, but it turns out it will notice your node\_modules folder and run from that instead if one exists:
% npx tsc --watch
Running this in Visual Studio Code
VSCode has built-in TypeScript support. Hit Shift+Command+B and select the tsc: watch option and it runs that watch command in a embedded terminal pane inside the editor itself.
" https://diigo.com/0rowgj
```
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