Typechecking With PropTypes
Note:
React.PropTypes
has moved into a different package since React v15.5. Please use theprop-types
library instead.We provide a codemod script to automate the conversion.
As your app grows, you can catch a lot of bugs with typechecking. For some applications, you can use JavaScript extensions like Flow or TypeScript to typecheck your whole application. But even if you don’t use those, React has some built-in typechecking abilities. To run typechecking on the props for a component, you can assign the special propTypes
property:
import PropTypes from 'prop-types';
class Greeting extends React.Component {
render() {
return (
<h1>Hello, {this.props.name}</h1>
);
}
}
Greeting.propTypes = {
name: PropTypes.string
};
In this example, we are using a class component, but the same functionality could also be applied to function components, or components created by React.memo
or React.forwardRef
.
PropTypes
exports a range of validators that can be used to make sure the data you receive is valid. In this example, we’re using PropTypes.string
. When an invalid value is provided for a prop, a warning will be shown in the JavaScript console. For performance reasons, propTypes
is only checked in development mode.
PropTypes
Here is an example documenting the different validators provided:
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.'
);
}
})
};
Requiring Single Child
With PropTypes.element
you can specify that only a single child can be passed to a component as children.
import PropTypes from 'prop-types';
class MyComponent extends React.Component {
render() {
// This must be exactly one element or it will warn.
const children = this.props.children;
return (
<div>
{children}
</div>
);
}
}
MyComponent.propTypes = {
children: PropTypes.element.isRequired
};
Default Prop Values
You can define default values for your props
by assigning to the special defaultProps
property:
class Greeting extends React.Component {
render() {
return (
<h1>Hello, {this.props.name}</h1>
);
}
}
// Specifies the default values for props:
Greeting.defaultProps = {
name: 'Stranger'
};
// Renders "Hello, Stranger":
ReactDOM.render(
<Greeting />,
document.getElementById('example')
);
If you are using a Babel transform like plugin-proposal-class-properties (previously plugin-transform-class-properties), you can also declare defaultProps
as static property within a React component class. This syntax has not yet been finalized though and will require a compilation step to work within a browser. For more information, see the class fields proposal.
class Greeting extends React.Component {
static defaultProps = {
name: 'stranger'
}
render() {
return (
<div>Hello, {this.props.name}</div>
)
}
}
The defaultProps
will be used to ensure that this.props.name
will have a value if it was not specified by the parent component. The propTypes
typechecking happens after defaultProps
are resolved, so typechecking will also apply to the defaultProps
.
Function Components
If you are using function components in your regular development, you may want to make some small changes to allow PropTypes to be properly applied.
Let’s say you have a component like this:
export default function HelloWorldComponent({ name }) {
return (
<div>Hello, {name}</div>
)
}
To add PropTypes, you may want to declare the component in a separate function before exporting, like this:
function HelloWorldComponent({ name }) {
return (
<div>Hello, {name}</div>
)
}
export default HelloWorldComponent
Then, you can add PropTypes directly to the HelloWorldComponent
:
import PropTypes from 'prop-types'
function HelloWorldComponent({ name }) {
return (
<div>Hello, {name}</div>
)
}
HelloWorldComponent.propTypes = {
name: PropTypes.string
}
export default HelloWorldComponent