Playground should run compiler as emitDeclarationOnly when in JS mode

[thw0rted]

Search Terms

playground, allowJS, emitDeclarationOnly

Suggestion

Right now if you set the Playground "Lang" to JavaScript, the right side (output) pane just shows a comment about not needing to compile because the source is JS. Instead, it should default to running tsc --allowJS --emitDeclarationOnly so that we can see the .d.ts file that would be created for the source.

Use Cases

Now that the compiler can be used to create typings based on JSDoc comments in JS code, it would be helpful to have an online sandbox for illustrating how certain JSDoc directives work. For example, if I want to open an issue here about a JSDoc feature misbehaving or some syntax that I'd like to see supported, being able to just put the code up on Playground would make things much easier for everyone involved.

Examples

When I run tsc with the emitDeclarationOnly flag, I get a typings file that I can include when consuming the (JS) code from TS. Playground should generate and show that file.

If implemented we could have a helpful online example of e.g. microsoft/TypeScript#31410, microsoft/TypeScript#30624, etc

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.

[orta]

A better explanation of #59

[orta]

Fixed by orta/typescript-play#35

[orta]

Thanks! I needed a fresh kick to think about that one