Typescript type annotations as comments

Typescript’s goal is simply be Javascript + Types.

There are many use cases where one might want to use the excellent typechecker but not really have any emit stage.

Projects already written in javascript work with allowJS. Typescript already supports parsing types from jsdoc comments.

What would be really awesome is just comment annotating your javascript with types and the project gets the benefit of being type checked. This could be a boon for a lot of existing javascript projects. Getting intellisense, VSCode typechecking on the fly and a lot of language server awesomeness.

e.g.

/// <reference path="..." />

class Hello {
    /*:: private*/ hello(message /*: string*/) /*: Promise<{}>*/{
                const promise /*: Promise<void>*/ = null 
        return /*:: <Promise<{}>>*/ null;
    }
}

i.e

/: [type] */ /:: [tscode] */

[abenhamdine]

IMHO, I think this feature is not very necessary (and this is also for future readers who would were eagerly looking for this feature).

At the beginning, I was also shy to add a compilation step in our projects, and considered using Flow only for the benefit of comment syntax. But a few tries whith ts, I realized that :

• the compilation step in Typescript is quite fast, simple and reliable
• the js code generate is very readable. Actually, the code transpiled by Typescript is nearly the same that i would have written ! (minus some line breaks removed, etc…). It means that if you want, at any moment, you could stop using ts, and revert back to the js files.

Otherwise, you juste have to rename .js file to .ts file in order to have type checking.

FWIW, our project is a very complex application developped with node and extjs, and we migrate nearly 60% of server code to Typescript in 2 weeks.

[mleg]

Dear core typescript developers, thank you for such a high quality tool you made. But if you only could imagine how we, typescript users, desperately need the feature discussed… You’ve done so much and what’s left is so little.