# Easy access to the compiler API

TypeScript VFS lets you create a self-contained TypeScript environment entirely under your control. This library is used to power the Playground, and provides the underlying tooling for [twoslash](/content/dev/twoslash/index.html) code samples.

There are 3 main uses for TypeScript VFS:

- Creating a TypeScript Program as an entry-point to the compiler API
- Running TypeScript to emit files like `*.js`, `*.d.ts` or `*.map`
- Using TypeScript's language service to make the same calls an editor would make

You can learn more in the [TypeScript VFS README](https://github.com/microsoft/TypeScript-Website/blob/v2/packages/typescript-vfs/)

### Setup with TypeScript from node_modules

```javascript
import ts from 'typescript'
import tsvfs from '@typescript/vfs'

const fsMap = tsvfs.createDefaultMapFromNodeModules({ target: ts.ScriptTarget.ES2015 })
fsMap.set('index.ts', 'console.log("Hello World")')
// ....
```

### Use the TypeScript CDN to get your lib.d.ts files

```javascript
import ts from 'typescript'
import tsvfs from '@typescript/vfs'

const fsMap = await tsvfs.createDefaultMapFromCDN(compilerOptions, ts.version, true, ts)
fsMap.set('index.ts', 'console.log("Hello World")')

const system = tsvfs.createSystem(fsMap)
const host = tsvfs.createVirtualCompilerHost(system, compilerOptions, ts)

const program = ts.createProgram({
  rootNames: [...fsMap.keys()],
  options: compilerOptions,
  host: host.compilerHost,
})

// This will update the fsMap with new files
// for the .d.ts and .js files
program.emit()

// Now I can look at the AST for the .ts file too
const index = program.getSourceFile('index.ts')
```