Create and run a TypeScript project

Let’s create the project we’ll use throughout the course.

Create a directory and initialize Bun inside it:

mkdir bun-notes
cd bun-notes
bun init --yes

bun init creates a small TypeScript project. The exact files may change as Bun evolves, but you should see package.json, tsconfig.json, and index.ts.

Replace the contents of index.ts with this:

const message: string = 'Hello from Bun'

console.log(message)

Run the file:

bun index.ts

Bun prints:

Hello from Bun

Bun transpiles TypeScript while it loads the file. We did not run tsc first, and we did not create a JavaScript copy.

Notice the word transpiles. Bun removes TypeScript syntax so the runtime can execute the program. This does not mean Bun performs a complete type check before every run.

Keep your editor’s TypeScript checks enabled. For a separate command-line type check, install TypeScript and run tsc --noEmit:

bun add --dev typescript
bunx tsc --noEmit

Running code and checking types are two different jobs. Keeping that distinction clear prevents a successful bun index.ts command from giving us false confidence about the types.