As compilation (er…transpilation) becomes the defacto standard of the post ES5, JSX-leaning JS dev landscape—care of tools like Babel—there is a growing sentiment that it may be time to let go of our fair language’s dynamic and coercive ways in favor of a more sensible, statically-typed way of doing things.

Which leads to questions like, “Sure, but where do I even start?”

The biggest camps are TypeScript (Microsoft) and Flow (Facebook), but if you’re working in React you’ve already got a wonderful, low-maintenance alternative in your codebase that’s as easy to implement as it is to learn.

import React, { PropTypes } from 'react';

Say hello to React.PropTypes, a developer-friendly tool for declaring and checking types. Sure, it handles all the primitives ( array, bool, func, number, object, string, symbol) easily enough:

function Nest({name}) {
  return (
    <div>
      We called it {name}.
    </div>
  );
}

Nest.propTypes = {
  name: PropTypes.string,
}

export default Nest;

But there’s also enough depth under the hood to manage some pretty sophisticated verifications:

Nest.propTypes = {
  name: PropTypes.string,
  eggs: PropTypes.shape({
    species: PropTypes.string,
    femaleToMale: PropTypes.arrayOf(PropTypes.number),
    hobbies: PropTypes.oneOf(['swimming', 'stalking']),
  }),
}

All-in you get nine additional types to throw your props against:

• node and element for all your DOM and React element needs
• instanceOf for digging into prototypes
• oneOf for lists of known potential values
• oneOfType for lists of known potential types
• arrayOf and objectOf for arrays and objects composed of a single type
• shape for objects in the shape of a specific schema
• and any for when you really don’t want to check for a type

Furthermore, you can attach isRequired to any PropType declaration for added rigidity.

hobbies: PropTypes.oneOf(['swimming', 'stalking']).isRequired

Couple things to note, PropType checking is disabled in production, and it’s only present as a guiding hand in development mode. It throws warnings, not errors.

👉 That’s it. You’re a type checking expert now. Don’t abuse this new power in opinion convos.