PropTypes

Every React app will be composed of an hierarchical tree of components that have different props, certainly then we will need to define and structure our props , to avoid bugs and errors .

Just as a function may have required arguments, a React component may require a prop to be defined in order to render properly. If you fail to pass a required prop into a component that requires it, your app may behave unexpectedly.

Lets take the example below

import  * as React from "react";
import ReactDOM from "react-dom";

const Alert =(props) => {
const {title,importantMessage,riskNumber,total=Math.max(1, riskNumber)} =props
  return (
    <div className="alert">
      <h1>{title}</h1>
      <h2>{importantMessage}</h2>
      <span>{ Math.round(riskNumber / total * 100) }%</span>
    </div>
  );
}
const rootElement = document.getElementById("root");
ReactDOM.render(
    <Alert title="danger zone" importantMessage="This is very dangerous" riskNumber={70}/>
  rootElement
);

This alert component requires four props for proper rendering: title,importantMessage ,riskNumber, and total. Default values are set for total prop in case they are not provided.

Based on what we see we can conclude that title and importantMessage props are expected to be a string. In the same vein, riskNumber and total are required to be numeric values because they are used for computing percent. Also, total is expected to never be 0 since it is being used as a divisor.

But what if we define the props with wrong types like this

import  * as React from "react";
import ReactDOM from "react-dom";

const Alert =(props) => {
const {title,importantMessage,riskNumber,total=Math.max(1, riskNumber)} =props
  return (
    <div className="alert">
      <h1>{title}</h1>
      <h2>{importantMessage}</h2>
      <span>{ Math.round(riskNumber / total * 100) }%</span>
    </div>
  );
}
const rootElement = document.getElementById("root");
ReactDOM.render(
<>   
 <Alert title="Error zone" importantMessage="This is very dangerous" riskNumber={func=>func} total={0}/>
 <Alert title="Error zone" importantMessage="This is very dangerous" riskNumber={70} total="0"/>
</>,
  rootElement
);

The app will render with invalid props, try to imagine this problem in a big complex app , that's why we needed to find a solution to define props type and keep the sanity of the developers

Proptypes

PropTypes is React’s internal mechanism for adding type checking to components.

React components use a special property named propTypes to set up type checking.

/**
 * FORFUNCTIONAL COMPONENTS
 */
function ReactComponent(props) {
  // ...implement render logic here
}

ReactComponent.propTypes = {
  // ...prop type definitions here
}


/**
 * CLASS COMPONENTS: METHOD 1
 */
class ReactComponent extends React.Component {
  // ...component class body here
}

ReactComponent.propTypes = {
  // ...prop type definitions here
}


/**
 * CLASS COMPONENTS: METHOD 2
 * Using the `static` class properties syntax
 */
class ReactComponent extends React.Component {
  // ...component class body here
  
  static propTypes = {
    // ...prop type definitions here
  }
}

When props are passed to a React component, they are checked against the type definitions configured in the propTypes property. When an invalid value is passed for a prop, a warning is displayed on the JavaScript console.

So how can i create a prototype validation for Alert component props .let's take a look at the code below :

const Alert = (props) => {
  const {
    title,
    importantMessage,
    riskNumber,
    total = Math.max(1, riskNumber)
  } = props;
  return (
    <div className="alert">
      <h1>{title}</h1>
      <h2>{importantMessage}</h2>
      <span>{Math.round((riskNumber / total) * 100)}%</span>
    </div>
  );
};

Alert.propTypes = {
  title(props, propName, componentName) {
    const type = typeof props[propName];
    if (type !== "string") {
      return new Error(
        `Prop ${propName} on the component ${componentName} must be of type string`
      );
    }
  }
};

Alert.propTypes it's an object that react reference when it render a component with props and pass each one of them to a validation function that we provide

Her we have validated the title prop to be always of type string

Alert.propTypes = {
  title(props, propName, componentName) {
    const type = typeof props[propName];
    if (type !== "string") {
      return new Error(
        `Prop ${propName} on the component ${componentName} must be of type string`
      );
    }
  }
};

And here you go a custom error for in our console to alert us of prop validation problems

we can even push it forward by creating an object that define generic validation like defining a generic error for every prop that need to be string or number:

const prototypes = {
  string(props, propName, componentName) {
    const type = typeof props[propName];
    if (type !== "string") {
      return new Error(
        `Prop ${propName} on the component ${componentName} must be of type string`
      );
    }
  },
  number(props, propName, componentName) {
    const type = typeof props[propName];
    console.log(type);
    if (type !== "number") {
      return new Error(
        `Prop ${propName} on the component ${componentName} must be of type number`
      );
    }
  }
};
const Alert = (props) => {
  const {
    title,
    importantMessage,
    riskNumber,
    total = Math.max(1, riskNumber)
  } = props;
  return (
    <div className="alert">
      <h1>{title}</h1>
      <h2>{importantMessage}</h2>
      <>{Math.round((riskNumber / total) * 100)}%</>
    </div>
  );
};
Alert.propTypes = {
  title: prototypes.string,
  importantMessage: prototypes.string,
  riskNumber: prototypes.number,
  total: prototypes.number
};

Proptypes doesn't chip with production build for performance issues , as it's a tool for developer to maintain and structure the code , it's not necessarily to have it on production either way

Prop-types package

npm: prop-typesnpm

It will always be nicer if we had pre built validators for our props , as it will be a little bit tedious to define prop types over and over again, and here come prop-type package

Prior to React 15.5.0, a utility named PropTypes was available as part of the React package, which provided a lot of validators for configuring type definitions for component props. It could be accessed with React.PropTypes.

However, in later versions of React, this utility has been moved to a separate package named prop-types, so you need to add it as a dependency for your project in order to get access to the PropTypes utility.

npm install prop-types --save
yarn add prop-types 

It can be imported into your project files as follows:

import PropTypes from 'prop-types';

To learn more about how you can use prop-types, how it differs from using React.PropTypes, and all the available validators, see the official prop-types documentation.

import PropTypes from 'prop-types';
const Alert = (props) => {
  const {
    title,
    importantMessage,
    riskNumber,
    total = Math.max(1, riskNumber)
  } = props;
  return (
    <div className="alert">
      <h1>{title}</h1>
      <h2>{importantMessage}</h2>
      <>{Math.round((riskNumber / total) * 100)}%</>
    </div>
  );
};

Alert.propTypes = {
  title: propTypes.string,
  importantMessage: propTypes.string,
  riskNumber: propTypes.number,
  total: propTypes.number
};

React PropTypes validators

The PropTypes utility exports a wide range of validators for configuring type definitions. Below we’ll list the available validators for basic, renderable, instance, multiple, collection, and required prop types.

Basic types

Below are the validators for the basic data types.

• PropTypes.any: The prop can be of any data type

• PropTypes.bool: The prop should be a Boolean

• PropTypes.number: The prop should be a number

• 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

Component.propTypes = {
  anyProp: PropTypes.any,
  booleanProp: PropTypes.bool,
  numberProp: PropTypes.number,
  stringProp: PropTypes.string,
  functionProp: PropTypes.func
}

Renderable types

PropTypes also exports the following validators for ensuring that the value passed to a prop can be rendered by React.

• PropTypes.node: The prop should be anything that can be rendered by React — a number, string, element, or array (or fragment) containing these types

• PropTypes.element: The prop should be a React element

Component.propTypes = {
  nodeProp: PropTypes.node,
  elementProp: PropTypes.element
}

One common usage of the PropTypes.element validator is in ensuring that a component has a single child. If the component has no children or multiple children, a warning is displayed on the JavaScript console.

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

Instance types

In cases where you require a prop to be an instance of a particular JavaScript class, you can use the PropTypes.instanceOf validator. This leverages the underlying JavaScript instanceof operator.

Component.propTypes = {
  personProp: PropTypes.instanceOf(Person)
}

Multiple types

PropTypes also exports validators that can allow a limited set of values or multiple sets of data types for a prop. Here they are:

• PropTypes.oneOf: The prop is limited to a specified set of values, treating it like an enum

• PropTypes.oneOfType: The prop should be one of a specified set of types, behaving like a union of types

Component.propTypes = {

  enumProp: PropTypes.oneOf([true, false, 0, 'Unknown']),
  
  unionProp: PropTypes.oneOfType([
    PropType.bool,
    PropType.number,
    PropType.string,
    PropType.instanceOf(Person)
  ])
  
}

Collection types

Besides thePropTypes.array and PropTypes.object validators, PropTypes also provides validators for more fine-tuned validation of arrays and objects.

PropTypes.arrayOf

PropTypes.arrayOf ensures that the prop is an array in which all items match the specified type.

Component.propTypes = {

  peopleArrayProp: PropTypes.arrayOf(
    PropTypes.instanceOf(Person)
  ),
  
  multipleArrayProp: PropTypes.arrayOf(
    PropTypes.oneOfType([
      PropType.number,
      PropType.string
    ])
  )
  
}

PropTypes.objectOf

PropTypes.objectOf ensures that the prop is an object in which all property values match the specified type.

Component.propTypes = {

  booleanObjectProp: PropTypes.objectOf(
    PropTypes.bool
  ),
  
  multipleObjectProp: PropTypes.objectOf(
    PropTypes.oneOfType([
      PropType.func,
      PropType.number,
      PropType.string,
      PropType.instanceOf(Person)
    ])
  )
  
}

PropTypes.shape

You can use PropTypes.shape when a more detailed validation of an object prop is required. It ensures that the prop is an object that contains a set of specified keys with values of the specified types.

Component.propTypes = {
  profileProp: PropTypes.shape({
    id: PropTypes.number,
    fullname: PropTypes.string,
    gender: PropTypes.oneOf(['M', 'F']),
    birthdate: PropTypes.instanceOf(Date),
    isAuthor: PropTypes.bool
  })
}

PropTypes.exact

For strict (or exact) object matching, you can use PropTypes.exact as follows:

Component.propTypes = {
  subjectScoreProp: PropTypes.exact({
    subject: PropTypes.oneOf(['Maths', 'Arts', 'Science']),
    score: PropTypes.number
  })
}

Required types

The PropTypes validators we’ve explored so far all allow the prop to be optional. However, you can chain isRequired to any prop validator to ensure that a warning is shown whenever the prop is not provided.

Component.propTypes = {

  requiredAnyProp: PropTypes.any.isRequired,
  requiredFunctionProp: PropTypes.func.isRequired,
  requiredSingleElementProp: PropTypes.element.isRequired,
  requiredPersonProp: PropTypes.instanceOf(Person).isRequired,
  requiredEnumProp: PropTypes.oneOf(['Read', 'Write']).isRequired,
  
  requiredShapeObjectProp: PropTypes.shape({
    title: PropTypes.string.isRequired,
    date: PropTypes.instanceOf(Date).isRequired,
    isRecent: PropTypes.bool
  }).isRequired
  
}

Custom validators for type-checking React props

Usually, you need to define some custom validation logic for component props — e.g., ensuring that a prop is passed a valid email address. prop-types allows you to define custom validation functions that can be used for type checking props.

Basic custom validators

The custom validation function takes three arguments:

1. props, an object containing all the props passed to the component

2. propName, the name of the prop to be validated

3. componentName, the name of the component

If the validation fails, it should return an Error object. The error should not be thrown. Also, console.warn should not be used inside the custom validation function.

const isEmail = function(props, propName, componentName) {
  const regex = /^((([^<>()[]\.,;:s@"]+(.[^<>()[]\.,;:s@"]+)*)|(".+"))@(([[0-9]{1,3}.[0-9]{1,3}.[0-9]{1,3}.[0-9]{1,3}])|(([a-zA-Z-0-9]+.)+[a-zA-Z]{2,})))?$/;
  
  if (!regex.test(props[propName])) {
    return new Error(`Invalid prop `${propName}` passed to `${componentName}`. Expected a valid email address.`);
  }
}

Component.propTypes = {
  email: isEmail,
  fullname: PropTypes.string,
  date: PropTypes.instanceOf(Date)
}

Custom validation functions can also be used with PropTypes.oneOfType. Here is a simple example using the isEmail custom validation function in the previous code snippet:

Component.propTypes = {
  email: PropTypes.oneOfType([
    isEmail,
    PropTypes.shape({
      address: isEmail
    })
  ])
}

Component will be valid in both of these scenarios:

<Component email="[e-mail]" />
<Component email={{ address: '[e-mail]' }} />

Custom validators and collections

Custom validation functions can also be used with PropTypes.arrayOf and PropTypes.objectOf. When used this way, the custom validation function are called for each key in the array or object.

However, the custom validation function takes five arguments instead of three:

1. propValue, the array or object itself

2. key, the key of the current item in the iteration

3. componentName, the name of the component

4. location, the location of the validated data (usually “prop”)

5. propFullName, the fully resolved name of the current item being validated. For an array, this will be array[index]; for an object, it will be object.key

Below is a modified version of the isEmail custom validation function for use with collection types.

const isEmail = function(propValue, key, componentName, location, propFullName) {
  const regex = /^((([^<>()[]\.,;:s@"]+(.[^<>()[]\.,;:s@"]+)*)|(".+"))@(([[0-9]{1,3}.[0-9]{1,3}.[0-9]{1,3}.[0-9]{1,3}])|(([a-zA-Z-0-9]+.)+[a-zA-Z]{2,})))?$/;
  
  if (!regex.test(propValue[key])) {
    return new Error(`Invalid prop `${propFullName}` passed to `${componentName}`. Expected a valid email address.`);
  }
}

Component.propTypes = {
  emails: PropTypes.arrayOf(isEmail)
}

All-purpose custom validators

Taking all we’ve learned about custom validation functions into account, let’s go ahead and create all-purpose custom validators that can be used as standalone validators and also with collection types.

A slight modification to the isEmail custom validation function will make it an all-purpose validator, as shown below.

const isEmail = function(propValue, key, componentName, location, propFullName) {
  // Get the resolved prop name based on the validator usage
  const prop = (location && propFullName) ? propFullName : key;
  
  const regex = /^((([^<>()[]\.,;:s@"]+(.[^<>()[]\.,;:s@"]+)*)|(".+"))@(([[0-9]{1,3}.[0-9]{1,3}.[0-9]{1,3}.[0-9]{1,3}])|(([a-zA-Z-0-9]+.)+[a-zA-Z]{2,})))?$/;
  
  if (!regex.test(propValue[key])) {
    return new Error(`Invalid prop `${prop}` passed to `${componentName}`. Expected a valid email address.`);
  }
}

Component.propTypes = {
  email: PropTypes.oneOfType([
    isEmail,
    PropTypes.shape({
      address: isEmail
    })
  ]),
  emails: PropTypes.arrayOf(isEmail)
}

Typechecking With PropTypes – React

I intensively use Typescript for all what concerns Types and types checking , and with that and i don't ever use proptypes in my projects , but it's always good to have such an amazing features on your grasp