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125 lines
3.7 KiB
Markdown
125 lines
3.7 KiB
Markdown
---
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title: React TypeChecking with PropTypes
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---
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## React PropTypes
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These serve as a method of typechecking. As an application grows, it tends to gather a fair amount of bugs. Typechecking with PropTypes can prevent those.
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## How to get PropTypes
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Starting with React version 15.5 this feature was moved to a separate package named prop-types.
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In order to use it, it's required to be added to the project as a dependency by issuing the following command in a console.
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```shell
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npm install --save prop-types
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```
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After that a whole range of validators that can be used to make sure the data the developer is going to recieve is actually valid.
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When an invalid value is provided there will be warning appearing in the JavaScript console.
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Note that for performance reasons the PropTypes defined are only checked while in development mode.
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Also on the contrary of the component state, that can be manipulated as needed, these props are readonly.
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It's value cannot be changed by the component.
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## PropTypes available
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Bellow is a code example with the different validators provided by the package, and how to inject them in the component.
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```javascript
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import PropTypes from 'prop-types';
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class MyComponent extends Component{
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constructor(props){
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super(props);
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}
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render(){
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return (
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...
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);
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}
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}
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MyComponent.propTypes = {
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// A prop that is a specific JS primitive. By default, these
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// are all optional.
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optionalArray: PropTypes.array,
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optionalBool: PropTypes.bool,
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optionalFunc: PropTypes.func,
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optionalNumber: PropTypes.number,
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optionalObject: PropTypes.object,
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optionalString: PropTypes.string,
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optionalSymbol: PropTypes.symbol,
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// Anything that can be rendered: numbers, strings, elements or an array
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// (or fragment) containing these types.
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optionalNode: PropTypes.node,
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// A React element as a PropType
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optionalElement: PropTypes.element,
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// Declaring that a prop is an instance of a class. This uses
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// JS's instanceof operator.
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optionalMessage: PropTypes.instanceOf(AnotherComponent),
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// You can ensure that your prop is limited to specific values by treating
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// it as an enum.
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optionalEnum: PropTypes.oneOf(['News', 'Photos']),
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// An object that could be one of many types
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optionalUnion: PropTypes.oneOfType([
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PropTypes.string,
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PropTypes.number,
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PropTypes.instanceOf(AnotherComponent)
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]),
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// An array of a certain type
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optionalArrayOf: PropTypes.arrayOf(PropTypes.number),
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// An object with property values of a certain type
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optionalObjectOf: PropTypes.objectOf(PropTypes.number),
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// An object taking on a particular shape
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optionalObjectWithShape: PropTypes.shape({
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color: PropTypes.string,
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fontSize: PropTypes.number
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}),
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// You can chain any of the above with `isRequired` to make sure a warning
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// is shown if the prop isn't provided.
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requiredFunc: PropTypes.func.isRequired,
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// A value of any data type
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requiredAny: PropTypes.any.isRequired,
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};
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```
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## Setting default values
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As a part of this feature it's also possible to define default values for any given component defined while developing.
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These make sure that the prop will have a value even if not specified by the parent component.
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The code bellow ilustrates how to use this funcionality.
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```javascript
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import React,{Component} from 'react';
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import PropTypes from 'prop-types';
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class MyComponent extends Component{
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constructor(props){
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super(props);
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}
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render(){
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return (
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<h3>Hello, {this.props.name}</h3>
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);
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}
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}
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MyComponent.defaultProps = {
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name: 'Stranger'
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};
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```
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For more information about PropTypes and other docs on React.
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Go to the [Official Site](https://reactjs.org/) and read the docs, or the [GitHub Repo](https://github.com/facebook/react/)
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