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 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.

Created 2020-09-06T09:36:03-07:00, updated 2020-09-06T10:29:54-07:00 · History · Edit