prop-types/README.md

# prop-types

Runtime type checking for React props and similar objects.

You can use prop-types to document the intended types of properties passed to
components. React (and potentially other libraries—see the checkPropTypes()
reference below) will check props passed to your components against those
definitions, and warn in development if they don’t match.

## Installation

```shell
npm install --save prop-types
```

## Importing

```js
import PropTypes from 'prop-types'; // ES6
var PropTypes = require('prop-types'); // ES5 with npm
```

### CDN

If you prefer to exclude `prop-types` from your application and use it
globally via `window.PropTypes`, the `prop-types` package provides
single-file distributions, which are hosted on the following CDNs:

* [**unpkg**](https://unpkg.com/prop-types/)
```html
<!-- development version -->
<script src="https://unpkg.com/prop-types@15.6/prop-types.js"></script>

<!-- production version -->
<script src="https://unpkg.com/prop-types@15.6/prop-types.min.js"></script>
```

* [**cdnjs**](https://cdnjs.com/libraries/prop-types)
```html
<!-- development version -->
<script src="https://cdnjs.cloudflare.com/ajax/libs/prop-types/15.6.0/prop-types.js"></script>

<!-- production version -->
<script src="https://cdnjs.cloudflare.com/ajax/libs/prop-types/15.6.0/prop-types.min.js"></script>
```

To load a specific version of `prop-types` replace `15.6.0` with the version number.

## Usage

PropTypes was originally exposed as part of the React core module, and is
commonly used with React components.
Here is an example of using PropTypes with a React component, which also
documents the different validators provided:

```js
import React from 'react';
import PropTypes from 'prop-types';

class MyComponent extends React.Component {
  render() {
    // ... do things with the props
  }
}

MyComponent.propTypes = {
  // You can declare that a prop is a specific JS primitive. 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,

  // 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),

  // You can chain any of the above with `isRequired` to make sure a warning
  // is shown if the prop isn't provided.

  // An object taking on a particular shape
  optionalObjectWithShape: PropTypes.shape({
    optionalProperty: PropTypes.string,
    requiredProperty: PropTypes.number.isRequired
  }),

  // An object with warnings on extra properties
  optionalObjectWithStrictShape: PropTypes.exact({
    optionalProperty: PropTypes.string,
    requiredProperty: PropTypes.number.isRequired
  }),

  requiredFunc: PropTypes.func.isRequired,

  // A 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.'
      );
    }
  })
};
```

Refer to the [React documentation](https://facebook.github.io/react/docs/typechecking-with-proptypes.html) for more information.

## Migrating from React.PropTypes

Check out [Migrating from React.PropTypes](https://facebook.github.io/react/blog/2017/04/07/react-v15.5.0.html#migrating-from-react.proptypes) for details on how to migrate to `prop-types` from `React.PropTypes`.

Note that this blog posts **mentions a codemod script that performs the conversion automatically**.

There are also important notes below.

## How to Depend on This Package?

For apps, we recommend putting it in `dependencies` with a caret range.
For example:

```js
  "dependencies": {
    "prop-types": "^15.5.7"
  }
```

For libraries, we *also* recommend leaving it in `dependencies`:

```js
  "dependencies": {
    "prop-types": "^15.5.7"
  },
  "peerDependencies": {
    "react": "^15.5.0"
  }
```

**Note:** there are known issues in versions before 15.5.7 so we recommend using it as the minimal version.

Make sure that the version range uses a caret (`^`) and thus is broad enough for npm to efficiently deduplicate packages.

For UMD bundles of your components, make sure you **don’t** include `PropTypes` in the build. Usually this is done by marking it as an external (the specifics depend on your bundler), just like you do with React.

## Compatibility

### React 0.14

This package is compatible with **React 0.14.9**. Compared to 0.14.8 (which was released a year ago), there are no other changes in 0.14.9, so it should be a painless upgrade.

```shell
# ATTENTION: Only run this if you still use React 0.14!
npm install --save react@^0.14.9 react-dom@^0.14.9
```

### React 15+

This package is compatible with **React 15.3.0** and higher.

```
npm install --save react@^15.3.0 react-dom@^15.3.0
```

### What happens on other React versions?

It outputs warnings with the message below even though the developer doesn’t do anything wrong. Unfortunately there is no solution for this other than updating React to either 15.3.0 or higher, or 0.14.9 if you’re using React 0.14.

## Difference from `React.PropTypes`: Don’t Call Validator Functions

First of all, **which version of React are you using**? You might be seeing this message because a component library has updated to use `prop-types` package, but your version of React is incompatible with it. See the [above section](#compatibility) for more details.

Are you using either React 0.14.9 or a version higher than React 15.3.0? Read on.

When you migrate components to use the standalone `prop-types`, **all validator functions will start throwing an error if you call them directly**. This makes sure that nobody relies on them in production code, and it is safe to strip their implementations to optimize the bundle size.

Code like this is still fine:

```js
MyComponent.propTypes = {
  myProp: PropTypes.bool
};
```

However, code like this will not work with the `prop-types` package:

```js
// Will not work with `prop-types` package!
var errorOrNull = PropTypes.bool(42, 'myProp', 'MyComponent', 'prop');
```

It will throw an error:

```
Calling PropTypes validators directly is not supported by the `prop-types` package.
Use PropTypes.checkPropTypes() to call them.
```

(If you see **a warning** rather than an error with this message, please check the [above section about compatibility](#compatibility).)

This is new behavior, and you will only encounter it when you migrate from `React.PropTypes` to the `prop-types` package. For the vast majority of components, this doesn’t matter, and if you didn’t see [this warning](https://facebook.github.io/react/warnings/dont-call-proptypes.html) in your components, your code is safe to migrate. This is not a breaking change in React because you are only opting into this change for a component by explicitly changing your imports to use `prop-types`. If you temporarily need the old behavior, you can keep using `React.PropTypes` until React 16.

**If you absolutely need to trigger the validation manually**, call `PropTypes.checkPropTypes()`. Unlike the validators themselves, this function is safe to call in production, as it will be replaced by an empty function:

```js
// Works with standalone PropTypes
PropTypes.checkPropTypes(MyComponent.propTypes, props, 'prop', 'MyComponent');
```
See below for more info.

**You might also see this error** if you’re calling a `PropTypes` validator from your own custom `PropTypes` validator. In this case, the fix is to make sure that you are passing *all* of the arguments to the inner function. There is a more in-depth explanation of how to fix it [on this page](https://facebook.github.io/react/warnings/dont-call-proptypes.html#fixing-the-false-positive-in-third-party-proptypes). Alternatively, you can temporarily keep using `React.PropTypes` until React 16, as it would still only warn in this case.

If you use a bundler like Browserify or Webpack, don’t forget to [follow these instructions](https://reactjs.org/docs/optimizing-performance.html#use-the-production-build) to correctly bundle your application in development or production mode. Otherwise you’ll ship unnecessary code to your users.

## PropTypes.checkPropTypes

React will automatically check the propTypes you set on the component, but if
you are using PropTypes without React then you may want to manually call
`PropTypes.checkPropTypes`, like so:

```js
const myPropTypes = {
  name: PropTypes.string,
  age: PropTypes.number,
  // ... define your prop validations
};

const props = {
  name: 'hello', // is valid
  age: 'world', // not valid
};

// Let's say your component is called 'MyComponent'

// Works with standalone PropTypes
PropTypes.checkPropTypes(myPropTypes, props, 'prop', 'MyComponent');
// This will warn as follows:
// Warning: Failed prop type: Invalid prop `age` of type `string` supplied to
// `MyComponent`, expected `number`.
```