`PropTypes` are a library for runtime type checking of props for React components. It was originally part of the React core, but split out into a separate library with React 16.

PropTypes are used for a combination of debugging during development ("you accidentally passed a string instead of a number", or "you forgot to include a required prop"), as well as documentation for a component. React devs have traditionally used PropTypes to act as readable documentation of a component's expected props, and there are tools that can extract PropTypes usages and generate documentation files.

However, with the rise of TS and Flow as static type systems, the need for a runtime-based type checker has gone down, especially since people using TS/Flow have probably already declared types for a given component's props.

I believe they’re referring to the PropTypes Library that grew out of React. It’s extremely limited in scope compared to something like TypeScript, but it does give you some benefit.

https://www.npmjs.com/package/prop-types

github.com/facebook/prop-types is the 2nd google search result for this term, and is what I was referring to, although the first result (devhints.io/react#property-validation) is arguably a better summary.

Ie. ‘lite’ type checking, used in react.

(did you perhaps see the results for ‘javascript prop type hint’ as a google autocorrect suggestion or something? This is a well known term, but I’m pretty amazed two seconds of google didn’t discover what it was...)

I read it and thought you were referring to something related to some proptype based code completion. The use of 'hinting' threw me off completely, especially when you're talking about checking & validating.

Yes I found the prop-types library, but it doesn't include the word "hint" and I couldn't find any documentation that did. I assumed there this was an obscure term of art you were refering to.