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React Workshop: Core concepts of react
- 2. React Js React is a javascript library for building interactive User Interface( UI ). 2
- 3. 3 Lorem Ipsum Lorem IpsumLorem Ipsum Lorem Ipsum Lorem Ipsum Lorem Ipsum Lorem Ipsum Lorem Ipsum Lorem Ipsum Root Element <html> Element <body> Element <head> Element <title> Element <h1> Element <p> Text Node “Page title” Text Node “My heading” Text Node “My Paragraph DOM
- 4. What makes React so fast? 4
- 9. 9 Why is React fast?
- 10. 10 Why is React so fast?
- 11. What is a Virtual DOM? A Javascript Object that is a “virtual”, representation of the “real” DOM. 11
- 12. Why use react? ● Updates and renders only the elements that change/update in the DOM( hence quick rendering ) ● Build encapsulated components that manage their own state. ● React can also render on the server using Node and powerful mobile apps using react native. 12
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- 15. History of React ● Created by Jordan Walke, a software engineer at Facebook ● First deployed on Facebook's newsfeed in 2011 and later on Instagram.com in 2012 ● Open-sourced at JSConf US in May 2013 ● Facebook announced React Fiber, on April 18, 2017 ● React 360 V1.0.0 was released to the public on April 19, 2017 15
- 16. 1- Add React in a Minute (Using React Scripts ) 2- Using create-react-app Set up React App 16
- 17. Class Based Components Extend React Component Class and it requires us to use render() React Components Functional Based Components Are pure JavaScript function that accepts props as its argument, and returns some JSX 17 Components allow you to split the UI into independent reusable pieces of JS codes.
- 18. Class Based Components Functional Based Components 18
- 19. JSX ( JavaScript-XML ) ● JSX is a XML-like syntax extension to JavaScript that creates React elements. ● Its makes your code human readable, otherwise we had to use React.createElement() ● Gives us expressiveness of JavaScript along with HTML like template syntax. 19
- 20. Examples of using JSX 20
- 21. What is a component state? ● A State of a component is an object, that holds some information that may change throughout the component lifecycle. 21
- 22. State of a Component 22 Virtual DOM
- 23. State of a Component 23 Virtual DOM
- 24. State of a Component 24 Virtual DOM
- 25. State of a Component 25 Virtual DOM setState()
- 26. State of a Component 26 Virtual DOM setState()
- 27. State of a Component 27 Virtual DOM setState()
- 28. State of a Component 28 setState() patch Virtual DOM
- 29. What is a component state? ● A State of a component is an object, that holds some information that may change throughout the component lifecycle. ● We define initial state and then we just have to notify that the state is changed and the react will automatically render the those changes on the front end behind the scenes. ● Every time the state changes the changes get re rendered so the UI( front end ) changes automatically. 29
- 30. Props ● Props are inputs to components. ● Single values or objects containing a set of values that are passed to components on creation, using a naming convention similar to HTML-tag attributes ● They are used to: 1-Pass custom data to your component. 2-Trigger state changes. 30
- 31. Important Points ● React may batch multiple setState() calls into a single update for performance. ● Because this.props and this.state may be updated asynchronously, you should not rely on their values for calculating the next state ● State is local or encapsulated. It is not accessible to any component other than the one that owns and sets it. ● A component may choose to pass its state down as props to its child components ● Imagine a component tree as a waterfall of props, each component’s state is like an additional water source that joins it at an arbitrary point but also flows down 31
- 32. Difference between State & Props Props =Props is passed by the parent to the Child components -A component should never modify its own props Component State =State is managed within a component for internal communication - State can be modified using setState() and when value of state changes render() is called. 32 The props( properties ) and state are both JavaScript objects. Props are like an args of a function and states are like local variables inside the function
- 33. Component LifeCycle Mounting - Component is constructed with the given Props and default state. This is done inside constructor() -Component came into the DOM Updating - When the state of a component is updated 33 Every React Component has a lifecycle of its own, which has different stages. Unmounting - Component is removed from the page
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- 35. Constructor ● Overrides the constructor of React.Component ● Required only when we initialize state or bind methods. E.g. this.handleClick = this.handleClick.bind(this); ● Call super(props) before any other statement. ● Do not call setState() inside it 35
- 36. getDerivedStateFromProp s ● Invoked right before calling the render method ● Called both on the initial mount and on subsequent updates ● Should return an object to update the state, or null to update nothing. ● Rare use cases where the state depends on changes in props 36
- 37. ComponentDidMount ● Load data from a remote endpoint ● Calling setState() here will trigger an extra rendering, but it will happen before the browser updates the screen. 37
- 38. shouldComponentUpdate ● Exists as a performance optimization ● Not called for the initial render or when forceUpdate() is used. ● Use built-in PureComponent instead of writing shouldComponentUpdate() ● PureComponent performs a shallow comparison of props and state, and reduces the chance that you’ll skip a necessary update. 38
- 39. render ● Required method in a class component ● Should return React Elements ( JSX ) or Arrays and fragments or Portals or String and numbers or Booleans or null ● Should not modify component state ● It does not directly interact with the browser. 39
- 40. getSnapshotBeforeUpdat e ● Invoked right before the most recently rendered output is committed to e.g. the DOM ● Capture some information from the DOM (e.g. scroll position) before it is potentially changed ● Returned value will be passed as a parameter to componentDidUpdate() ● Example to use it: A chat thread that need to handle scroll position in a special way. 40
- 41. ComponentDidUpdate ● Invoked immediately after updating occurs. ● Calling setState() here will trigger an extra rendering, but it will happen before the browser updates the screen. ● setState() can be called but it must be wrapped in a condition. ● If getSnapshotBeforeUpdate() is implemented, snapshot param will be available, else undefined. 41
- 42. ComponentWillUnmount ● invoked immediately before a component is unmounted. ● For e.g. Invalidating timers, canceling network requests, or cleaning up any subscriptions. ● should not call setState() as component will never be rerendered. 42