doc: specificy support for erasable ts syntax · nodejs/node@888d2ac

The flag [`--no-experimental-strip-types`][] prevents Node.js from running TypeScript

files. By default Node.js will execute only files that contain no

TypeScript features that require transformation, such as enums or namespaces.

TypeScript features that require transformation, such as enums.

Node.js will replace inline type annotations with whitespace,

and no type checking is performed.

To enable the transformation of such features

The most prominent features that require transformation are:

* `Enum`

* `namespaces`

* `legacy module`

* `Enum` declarations

* `namespace` with runtime code

* legacy `module` with runtime code

* parameter properties

* import aliases

`namespaces` and `module` that do not contain runtime code are supported.

This example will work correctly:

```ts

// This namespace is exporting a type

namespace TypeOnly {

export type A = string;

}

```

This will result in [`ERR_UNSUPPORTED_TYPESCRIPT_SYNTAX`][] error:

```ts

// This namespace is exporting a value

namespace A {

export let x = 1

}

```

Since Decorators are currently a [TC39 Stage 3 proposal](https://github.com/tc39/proposal-decorators)

and will soon be supported by the JavaScript engine,

[CommonJS]: modules.md

[ES Modules]: esm.md

[Full TypeScript support]: #full-typescript-support

[`ERR_UNSUPPORTED_TYPESCRIPT_SYNTAX`]: errors.md#err_unsupported_typescript_syntax

[`--experimental-transform-types`]: cli.md#--experimental-transform-types

[`--no-experimental-strip-types`]: cli.md#--no-experimental-strip-types

[`tsconfig` "paths"]: https://www.typescriptlang.org/tsconfig/#paths