We define a custom function validator for the children property. Inside the function, we first use the built-in propTypes functions to check if children is an array of React elements. If the result of the validation is not an instance of Error, then we use the React Children's count utility method to know how many React elements were given and we return an error if the number of React elements in children is not 2.
- Title Page
- Copyright and Credits
- Packt Upsell
- Contributors
- Preface
- Introduction to the MERN Stack
- Building a Web server with ExpressJS
- Technical requirements
- Introduction
- Routing in ExpressJS
- Modular route handlers
- Writing middleware functions
- Writing configurable middleware functions
- Writing router-level middleware functions
- Writing error-handler middleware functions
- Using ExpressJS' built-in middleware function for serving static assets
- Parsing the HTTP request body
- Compressing HTTP responses
- Using an HTTP request logger
- Managing and creating virtual domains
- Securing an ExpressJS web application with Helmet
- Using template engines
- Debugging your ExpressJS web application
- Building a RESTful API
- Technical requirements
- Introduction
- CRUD operations using ExpressJS' route methods
- CRUD operations with Mongoose
- Using Mongoose query builders
- Defining document instance methods
- Defining static model methods
- Writing middleware functions for Mongoose
- Writing custom validators for Mongoose's schemas
- Building a RESTful API to manage users with ExpressJS and Mongoose
- Real-Time Communication with Socket.IO and ExpressJS
- Managing State with Redux
- Technical requirements
- Introduction
- Defining actions and action creators
- Defining reducer functions
- Creating a Redux store
- Binding action creators to the dispatch method
- Splitting and combining reducers
- Writing Redux store enhancers
- Time traveling with Redux
- Understanding Redux middleware
- Dealing with asynchronous data flow
- Building Web Applications with React
- Technical requirements
- Introduction
- Understanding React elements and React components
- Composing components
- Stateful components and life cycle methods
- Working with React.PureComponent
- React event handlers
- Conditional rendering of components
- Rendering lists with React
- Working with forms and inputs in React
- Understanding refs and how to use them
- Understanding React portals
- Catching errors with error boundary components
- Type checking properties with PropTypes
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