awesome-cheatsheets/frontend/react.js

/* *******************************************************************************************
 * REACT.JS CHEATSHEET
 * https://reactjs.org/
 * ******************************************************************************************* */


```
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
 * https://reactjs.org/docs/react-component.html
 * ******************************************************************************************* */



/* *******************************************************************************************
 * 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.'
      );
    }
  })
};

// Specifies the default values for props:
MyComponent.defaultProps = {
  name: 'Stranger'
};