export access modifiers

Search Terms

export access modifiers public protected private

Related: #321

Suggestion

Allow adding public, protected and private access modifiers to export statements. This would limit where the data can be imported from.

Access Modifiers

private

Other file in the same directory scope have access to the export.

protected

Other file in the same directory scope or a nested scope have access to the export.

public (default)

Current behavior - Can be access from anywhere.

Use Cases

Most useful for large projects - allows modules to limit where things they expose are used.

Examples

Given the following director structure:

.
├── module
│   ├── submodule
│   │   └── index.ts
│   ├── file.ts
│   └── index.ts
└── index.ts

// module/file.ts
public export const foo = "hello";
protected export const bar = "world";
private export const baz = "!!!";

// module/submodule/index.ts
import { foo, bar, baz } from '../file';
                // ^^^ Cannot access baz as is private.

// module/index.ts
import { foo, bar, baz } from './file'; // All Ok.

// index.ts
import { foo, bar, baz } from './module/file';
           // ^^^ Cannot access bar as is protected.
                // ^^^ Cannot access baz as is private.

Note: If using import * as X from ..., X's type simply wouldn't include things it doesn't have access to.

Checklist

My suggestion meets these guidelines:

• This wouldn't be a breaking change in existing TypeScript/JavaScript code
• This wouldn't change the runtime behavior of existing JavaScript code
• This could be implemented without emitting different JS based on the types of the expressions
• This isn't a runtime feature (e.g. library functionality, non-ECMAScript syntax with JavaScript output, etc.)
• This feature would agree with the rest of TypeScript's Design Goals.

Start by reviewing related issue #321 and the access-modifier examples in this issue. Define how directory and nested-scope access should be checked for direct imports and import * as before locating the relevant TypeScript compiler tests. Done means the proposed rules are specified and covered by tests without changing emitted JavaScript.