Basic Usage

TypeScript Twoslash is a pre-processor that enhances your code-samples. It is a markup language for JavaScript and TypeScript.

It leverages the compiler APIs used by text editors to offer type-driven hover information, precise error messages, and type callouts.

Using the homepage as an example, here is a simple code sample:

Before

```ts twoslash
// @errors: 2540

console.log((1 + 2 + 3 + 4).toFixed(2))
//                            ^|

/** A Basic Todo interface*/
interface Todo {
  title: string;
}

const todo: Readonly<Todo> = {
  title: 'Delete inactive users',
//  ^?
}

todo.title = 'Hello'
```

After

console.log((1 + 2 + 3 + 4).to Fixed(2))
toExponential
toFixed
toLocaleString
toPrecision
toString

/** A Basic Todo interface*/
interface Todo {
  title: string;
}

const todo: Readonly<Todo> = {
  title: 'Delete inactive users',
title: string
}

todo.title = 'Hello'
Error ts(2540)  ― Cannot assign to 'title' because it is a read-only property.