Setting up tsconfig.json

Using the TypeScript compiler (tsc) is the most simple way to get started. Probably simpler than any Babel-related setup you've ever used. tsc can be added to your PATH by globally installing TypeScript (npm i -g typescript).

tsc -w main.ts

... generates a main.js file in the same folder with default compiler settings. -w toggles the watch mode.

A simple project

Below we go through setting tsconfig.json for a simple project compiled using tsc. This is mostly commonly used in backend projects. If you are using a predefined build pack like "Create React App", "Next.js" or "Nest.js", this already comes set up. Also, those build configurations use javascript bundlers like "Webpack" or "SWC" instead of raw tsc.

For a project, it is recommended that you install TypeScript locally so that your project is tied to a specific TS version. In VSCode, tsc can be invoked through F1 > Run Build Task. You should also include a link for it in the package.json scripts.

tsc looks for a tsconfig.json file in the same folder. When a tsconfig is around, you can just call tsc without arguments. The tsconfig accepts an overwhelming set of compiler options -- since it mixes compiling and type checking options. Below I'll go through a set of recommended settings.

{
  "compilerOptions": {
    ...
  },
  "include: ["src"]
}

• include filters which files to compile. This can be a folder or an entry point (every file referenced by that entry point will also be compiled);

I will usually split input and output files in different folders:

|__ built
| |__ index.js
|__ src
| |__ index.ts
|__ tsconfig.json

• By default tsc outputs to the same folder the source files are. Use "outDir": "built" to fix that;

  "sourceMap": true

• Sourcemaps allow you to debug directly in the source .ts files.

  "target": "es2017",
  "module": "esnext",
  "esModuleInterop": true

Those 3 are output settings:

• target dictates how old is the runtime you want to support;

• module allows for import/export syntax conversion; You'd usually use "esnext" (no conversion*) when using a bundler, or "commonjs" for node;

• esModuleInterop is an es-modules "quirk" fix;

  "strict": true,
  "noImplicitAny": false,

Type-checking options:

• strict turns on all of the latest type-checking features (very important);

• noImplicitAny disables one specially annoying feature with a good trade-off (personal opinion);

  "lib": ["dom", "es2015", "es2017"],

• libis entirely optional and allows tuning of which global-environment types are available; For instance, the default setting includes "dom", but you'd like to disable "dom" types in a node.js project.

Concluding it, we got:

{
  "compilerOptions": {
    "target": "es2017",
    "module": "esnext",
    "esModuleInterop": true,
    "strict": true,
    "noImplicitAny": false,
    "lib": ["dom", "es2015", "es2017"],
    "outDir": "dist",
    "sourceMap": true
  },
  "include": ["src/index.ts"]
}