> Because the bits that aren’t typescript won’t warn you when you compile.

You just wrote exactly why static types are great: you get warnings when you forget to refactor your shitty (sic) JS code.

Typescript will happily check your JavaScript code with “allowJs” compiler flag.

We write all our new code in good ol ES6 flavor of JavaScript and typehint in jsdoc. Typescript as a typechecker serves as very well.

It’s a great incremental adoption strategy.

can you explain how this works ? this is very interesting to us. We have a large react app (created using create-react-app) in ES6 and have been considering adopting TS gradually.

This seems a great first step.

AFAIU, just add typescript to your project or globally then in your project set a tsconfig.json file with the allowJs and esModuleInterop flags set to true. Don’t quote me on this but you can probably leave out most of the rest of the flags besides your source location. For example:

    {
        “compilerOptions”: {
            “allowJs”: true,
            “esModuleInterop”: true
        },
        “include”: [ “src/**/*” ],
        “exclude”: [ “node_modules/**/*” ]
    }

You’ll probably have to tweak that, but I hope it helps.

https://www.typescriptlang.org/docs/handbook/compiler-option...

See https://github.com/Microsoft/TypeScript/wiki/JSDoc-support-i...

Also Google’s puppeteer project is typechecked with tsc and the type info is all in jsdocs

https://github.com/GoogleChrome/puppeteer

> I think it’s inferior because it allows you to rewrite only parts

That's exactly why it's superior, your project just becomes better step by step without an expensive and complicated full rewrite.