/* *******************************************************************************************
* REACT.JS CHEATSHEET
* DOCUMENTATION: https://reactjs.org/docs/
* FILE STRUCTURE: https://reactjs.org/docs/faq-structure.html
* ******************************************************************************************* */
```
npm install --save react // declarative and flexible JavaScript library for building UI
npm install --save react-dom // serves as the entry point of the DOM-related rendering paths
npm install --save prop-types // runtime type checking for React props and similar objects
```
// notes: don't forget the command lines
/* *******************************************************************************************
* REACT
* https://reactjs.org/docs/react-api.html
* ******************************************************************************************* */
// Create and return a new React element of the given type.
// Code written with JSX will be converted to use React.createElement().
// You will not typically invoke React.createElement() directly if you are using JSX.
React.createElement(
type,
[props],
[...children]
)
// Clone and return a new React element using element as the starting point.
// The resulting element will have the original element’s props with the new props merged in shallowly.
React.cloneElement(
element,
[props],
[...children]
)
// Verifies the object is a React element. Returns true or false.
React.isValidElement(object)
React.Children // provides utilities for dealing with the this.props.children opaque data structure.
// Invokes a function on every immediate child contained within children with this set to thisArg.
React.Children.map(children, function[(thisArg)])
// Like React.Children.map() but does not return an array.
React.Children.forEach(children, function[(thisArg)])
// Returns the total number of components in children,
// equal to the number of times that a callback passed to map or forEach would be invoked.
React.Children.count(children)
// Verifies that children has only one child (a React element) and returns it.
// Otherwise this method throws an error.
React.Children.only(children)
// Returns the children opaque data structure as a flat array with keys assigned to each child.
// Useful if you want to manipulate collections of children in your render methods,
// especially if you want to reorder or slice this.props.children before passing it down.
React.Children.toArray(children)
// The React.Fragment component lets you return multiple elements in a render() method without creating an additional DOM element
// You can also use it with the shorthand <></> syntax.
React.Fragment
/* *******************************************************************************************
* REACT.COMPONENT
* React.Component is an abstract base class, so it rarely makes sense to refer to React.Component
* directly. Instead, you will typically subclass it, and define at least a render() method.
* https://reactjs.org/docs/react-component.html
* ******************************************************************************************* */
class Component extends React.Component {
// Will be called before it is mounted
constructor(props) {
// Call this method before any other statement
// or this.props will be undefined in the constructor
super(props);
// The constructor is also often used to bind event handlers to the class instance.
// Binding makes sure the method has access to component attributes like this.props and this.state
this.method = this.method.bind(this);
// The constructor is the right place to initialize state.
this.state = {
active: true,
// In rare cases, it’s okay to initialize state based on props.
// This effectively “forks” the props and sets the state with the initial props.
// If you “fork” props by using them for state, you might also want to implement componentWillReceiveProps(nextProps)
// to keep the state up-to-date with them. But lifting state up is often easier and less bug-prone.
color: props.initialColor
};
}
// Enqueues changes to the component state and
// tells React that this component and its children need to be re-rendered with the updated state.
// setState() does not always immediately update the component. It may batch or defer the update until later.
// This makes reading this.state right after calling setState() a potential pitfall.
// Instead, use componentDidUpdate or a setState callback.
// You may optionally pass an object as the first argument to setState() instead of a function.
setState(updater[, callback]) { }
// Invoked just before mounting occurs (before render())
// This is the only lifecycle hook called on server rendering.
componentWillMount() { }
// Invoked immediately after a component is mounted.
// Initialization that requires DOM nodes should go here.
// If you need to load data from a remote endpoint, this is a good place to instantiate the network request.
// This method is a good place to set up any subscriptions. If you do that, don’t forget to unsubscribe in componentWillUnmount().
componentDidMount() { }
// Invoked before a mounted component receives new props.
// If you need to update the state in response to prop changes (for example, to reset it),
// you may compare this.props and nextProps and perform state transitions using this.setState() in this method.
componentWillReceiveProps(nextProps) { }
// Let React know if a component’s output is not affected by the current change in state or props.
// The default behavior is to re-render on every state change, and in the vast majority of cases you should rely on the default behavior.
// shouldComponentUpdate() is invoked before rendering when new props or state are being received. Defaults to true.
// This method is not called for the initial render or when forceUpdate() is used.
// Returning false does not prevent child components from re-rendering when their state changes.
shouldComponentUpdate(nextProps, nextState) { }
// Invoked just before rendering when new props or state are being received.
// Use this as an opportunity to perform preparation before an update occurs. This method is not called for the initial render.
// Note that you cannot call this.setState() here; nor should you do anything else
// (e.g. dispatch a Redux action) that would trigger an update to a React component before componentWillUpdate() returns.
// If you need to update state in response to props changes, use componentWillReceiveProps() instead.
componentWillUpdate(nextProps, nextState) { }
// Invoked immediately after updating occurs. This method is not called for the initial render.
// Use this as an opportunity to operate on the DOM when the component has been updated.
// This is also a good place to do network requests as long as you compare the current props to previous props (e.g. a network request may not be necessary if the props have not changed).
componentDidUpdate(prevProps, prevState) { }
// Invoked immediately before a component is unmounted and destroyed.
// Perform any necessary cleanup in this method, such as invalidating timers, canceling network requests,
// or cleaning up any subscriptions that were created in componentDidMount().
componentWillUnmount() { }
// Error boundaries are React components that catch JavaScript errors anywhere in their child component tree,
// log those errors, and display a fallback UI instead of the component tree that crashed.
// Error boundaries catch errors during rendering, in lifecycle methods, and in constructors of the whole tree below them.
componentDidCatch() { }
// This method is required.
// It should be pure, meaning that it does not modify component state,
// it returns the same result each time it’s invoked, and
// it does not directly interact with the browser (use lifecycle methods for this)
// It must return one of the following types: react elements, string and numbers, portals, null or booleans.
render() {
// Contains the props that were defined by the caller of this component.
console.log(this.props);
// Contains data specific to this component that may change over time.
// The state is user-defined, and it should be a plain JavaScript object.
// If you don’t use it in render(), it shouldn’t be in the state.
// For example, you can put timer IDs directly on the instance.
// Never mutate this.state directly, as calling setState() afterwards may replace the mutation you made.
// Treat this.state as if it were immutable.
console.log(this.state);
return (
<div>
{/* Comment goes here */}
Hello, {this.props.name}!
</div>
);
}
}
// Can be defined as a property on the component class itself, to set the default props for the class.
// This is used for undefined props, but not for null props.
Component.defaultProps = {
color: 'blue'
};
component = new Component();
// By default, when your component’s state or props change, your component will re-render.
// If your render() method depends on some other data, you can tell React that the component needs re-rendering by calling forceUpdate().
// Normally you should try to avoid all uses of forceUpdate() and only read from this.props and this.state in render().
component.forceUpdate(callback)
/* *******************************************************************************************
* REACT.DOM
* The react-dom package provides DOM-specific methods that can be used at the top level of
* your app and as an escape hatch to get outside of the React model if you need to.
* Most of your components should not need to use this module.
* https://reactjs.org/docs/react-dom.html
* ******************************************************************************************* */
// Render a React element into the DOM in the supplied container and return a reference
// to the component (or returns null for stateless components).
ReactDOM.render(element, container[, callback])
// Same as render(), but is used to hydrate a container whose HTML contents were rendered
// by ReactDOMServer. React will attempt to attach event listeners to the existing markup.
ReactDOM.hydrate(element, container[, callback])
// Remove a mounted React component from the DOM and clean up its event handlers and state.
// If no component was mounted in the container, calling this function does nothing.
// Returns true if a component was unmounted and false if there was no component to unmount.
ReactDOM.unmountComponentAtNode(container)
// If this component has been mounted into the DOM, this returns the corresponding native browser
// DOM element. This method is useful for reading values out of the DOM, such as form field values
// and performing DOM measurements. In most cases, you can attach a ref to the DOM node and avoid
// using findDOMNode at all.
ReactDOM.findDOMNode(component)
// Creates a portal. Portals provide a way to render children into a DOM node that exists outside
// the hierarchy of the DOM component.
ReactDOM.createPortal(child, container)
/* *******************************************************************************************
* REACTDOMSERVER
* The ReactDOMServer object enables you to render components to static markup.
* https://reactjs.org/docs/react-dom.html
* ******************************************************************************************* */
// Render a React element to its initial HTML. React will return an HTML string.
// You can use this method to generate HTML on the server and send the markup down on the initial
// request for faster page loads and to allow search engines to crawl your pages for SEO purposes.
ReactDOMServer.renderToString(element)
// Similar to renderToString, except this doesn’t create extra DOM attributes that React uses
// internally, such as data-reactroot. This is useful if you want to use React as a simple static
// page generator, as stripping away the extra attributes can save some bytes.
ReactDOMServer.renderToStaticMarkup(element)
// Render a React element to its initial HTML. Returns a Readable stream that outputs an HTML string.
// The HTML output by this stream is exactly equal to what ReactDOMServer.renderToString would return.
// You can use this method to generate HTML on the server and send the markup down on the initial
// request for faster page loads and to allow search engines to crawl your pages for SEO purposes.
ReactDOMServer.renderToNodeStream(element)
// Similar to renderToNodeStream, except this doesn’t create extra DOM attributes that React uses
// internally, such as data-reactroot. This is useful if you want to use React as a simple static
// page generator, as stripping away the extra attributes can save some bytes.
ReactDOMServer.renderToStaticNodeStream(element)
/* *******************************************************************************************
* TYPECHECKING WITH PROPTYPES
* https://reactjs.org/docs/typechecking-with-proptypes.html
* ******************************************************************************************* */
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,
// 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
}),
// 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 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.'
);
}
})
};