React Props Typechecking with PropTypes

Why validate props in React

React props, which stands for "properties", are read-only object being send from one component to another. Since Javascript is a dynamic language and doen't have a built-in type checking solution, a component doen't know props sent to it has correct type as it designed for. This can lead to bugs, or even worse, unexpected behaviors in a react app.

Many developers turned to TypeScript because it is a superset of Javascript and more important, it is strong typed. Fortunately, react has an internal mechanism for props type checking: PropTypes

Installation

Install the prop-types package via yarn or npm:

yarn add prop-types

and import this package into project files:

import PropTypes from 'prop-types';

Basic prop type validators

According to official docs, these are validators for the basic prop types:

  • PropTypes.bool: The prop should be a Boolean
  • PropTypes.number: The prop should be a number
  • PropTypes.any: The prop can be of any data type
  • PropTypes.string: The prop should be a string
  • PropTypes.func: The prop should be a function
  • PropTypes.array: The prop should be an array
  • PropTypes.object: The prop should be an object
  • PropTypes.symbol: The prop should be a symbol
  • PropTypes.node: The prop should be anything that can be rendered by React
    • ie. numbers, strings, elements can be rendered on screen, but not boolean
  • PropTypes.element: The prop should be a React element
    • ie. MyConponent
  • PropTypes.any: The prop can be anything

Usage

Ensure a prop is an object with specified type of values

MyComponent.propTypes = {
  objProp: PropTypes.shape({
    id: PropTypes.number,
    name: PropTypes.string,
    productSize: PropTypes.oneOf(['S', 'M', 'L']),
    birthdate: PropTypes.instanceOf(Date),
  })
}

Stric prop object matching

Component.propTypes = {
  objProp: PropTypes.exact({
    name: PropTypes.string,
    age: PropTypes.number,
  })
}

Make a prop required

MyComponent.propTypes = {
    propOne: PropTypes.any.isRequired,
    PropTwo: PropTypes.func.isRequired,
    objProp: PropTypes.Shape().isRequired
}

Ensure a component has a single child

MyComponent.propTypes = {
  children: PropTypes.element.isRequired
}

Ensure a prop to be an instance of a particular class

MyComponent.propTypes = {
  oneProp: PropTypes.instanceOf(MyClass)
}

Full use cases from offical docs

import PropTypes from 'prop-types';
MyComponent.propTypes = {
  // You can declare that a prop is a specific JS type. By default, these
  // are all optional.
  optionalArray: PropTypes.array,
  optionalBool: PropTypes.bool,
  optionalFunc: PropTypes.func,
  optionalNumber: PropTypes.number,
  optionalObject: PropTypes.object,
  optionalString: PropTypes.string,
  optionalSymbol: PropTypes.symbol,
  // Anything that can be rendered: numbers, strings, elements or an array
  // (or fragment) containing these types.
  optionalNode: PropTypes.node,
  // A React element.
  optionalElement: PropTypes.element,
  // A React element type (ie. MyComponent).
  optionalElementType: PropTypes.elementType,
  // You can also declare that a prop is an instance of a class. This uses
  // JS's instanceof operator.
  optionalMessage: PropTypes.instanceOf(Message),
  // You can ensure that your prop is limited to specific values by treating
  // it as an enum.
  optionalEnum: PropTypes.oneOf(['News', 'Photos']),
  // An object that could be one of many types
  optionalUnion: PropTypes.oneOfType([
    PropTypes.string,
    PropTypes.number,
    PropTypes.instanceOf(Message)
  ]),
  // An array of a certain type
  optionalArrayOf: PropTypes.arrayOf(PropTypes.number),
  // An object with property values of a certain type
  optionalObjectOf: PropTypes.objectOf(PropTypes.number),
  // An object taking on a particular shape
  optionalObjectWithShape: PropTypes.shape({
    color: PropTypes.string,
    fontSize: PropTypes.number
  }),
  // An object with warnings on extra properties
  optionalObjectWithStrictShape: PropTypes.exact({
    name: PropTypes.string,
    quantity: PropTypes.number
  }),   
  // You can chain any of the above with `isRequired` to make sure a warning
  // is shown if the prop isn't provided.
  requiredFunc: PropTypes.func.isRequired,
  // A required value of any data type
  requiredAny: PropTypes.any.isRequired,
  // You can also specify a custom validator. It should return an Error
  // object if the validation fails. Don't `console.warn` or throw, as this
  // won't work inside `oneOfType`.
  customProp: function(props, propName, componentName) {
    if (!/matchme/.test(props[propName])) {
      return new Error(
        'Invalid prop `' + propName + '` supplied to' +
        ' `' + componentName + '`. Validation failed.'
      );
    }
  },
  // You can also supply a custom validator to `arrayOf` and `objectOf`.
  // It should return an Error object if the validation fails. The validator
  // will be called for each key in the array or object. The first two
  // arguments of the validator are the array or object itself, and the
  // current item's key.
  customArrayProp: PropTypes.arrayOf(function(propValue, key, componentName, location, propFullName) {
    if (!/matchme/.test(propValue[key])) {
      return new Error(
        'Invalid prop `' + propFullName + '` supplied to' +
        ' `' + componentName + '`. Validation failed.'
      );
    }
  })
};