Is it possible to use custom type definitions in an ES6 project?

My team works on a relatively large NodeJS project, written in ES6, transpiled by babel, and then deployed as AWS lambdas with Serverless. This project is focused around consuming, mapping/transforming, and outputting one specific object type, which we have defined.

Our problem is, ECMA/JavaScript is not strongly typed, so if we make a mistake like treating a field as an array somewhere and a string somewhere else, there's nothing to catch that except runtime errors. We have also poorly documented the structure of this object, so sometimes consumers send us instances of the object with data in slightly misnamed fields that we say we process, but don't actually use.

I am looking for a way to create some kind of schema or type definition for this specific object in our project, so we can use that to correct our code, make our processing more robust, and create much better documentation for it. Now, I know VSCode offers some basic type checking in JavaScript, but I don't think it's feasible to try to JSDoc a really big object and then put that doc in every file that uses the object. I have found that VSCode can also, somehow, drive that checking with .d.ts files but I don't understand if or how I can leverage that for a specific, custom object that we've designed. Most of what I have found seems to be specifically related to pulling .d.ts files for external libraries.

So, TL:DR, Is it possible, in a NodeJS/ES6 project, to make one object, widely used throughout that project, strongly typed? Error checking in VSCode would be acceptable, but some kind of command-line linting that we could trigger before transpiling would be great too.

via cgm123