For example, with JavaScript + React, we can use React’s PropTypes for automated dynamic type checks in development mode, and even compile the type checks away for production deployment, since they’re no longer needed once you’ve verified that the correct types are being passed.
You Might Not Need TypeScript (or Static Types)
Eric Elliott

this is not strictly true, you are able to define new properties and state within your code so your list of property types could be inaccurate and incomplete.

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