Understanding React — Component life-cycle – Bartosz Szczeciński – Medium

Understanding React — Component life-cycle

☞ 

#Reactjs #programming

  • In all other instances remember to use this.setState – DO – set initial stateif not using class properties syntax — prepare all class fields and bind functions that will be passed as callbacksDON’T – cause any side effects (AJAX calls is a somehow special case — componentWillMount does not differ much from constructor -…
  • DO – update state via this.setStateperform last minute optimizationcause side-effects (AJAX calls etc.) in case of server-side-rendering onlyDON’T – cause any side effects (AJAX calls etc.) on client function will be called in each update life-cycle caused by changes to props (parent component re-rendering) and will be passed an object…
  • DO – use for increasing performance of poor performing ComponentsDON’T – cause any side effects (AJAX calls etc.)call nextState)If the shouldComponentUpdate function is not implemented, or it decided that the component should update in this render cycle, another life-cycle function will be called.
  • == this.props.myProp) { – // this.props.myProp has a different value – // we can perform any operations that would – // need the new value and/or cause side-effects – // like AJAX calls with the new value – this.props.myProp – } – }DO – cause side effects (AJAX calls etc.)DON’T…
  • DO – cause side effects (AJAX calls etc.)DON’T – call this.setState as it will result in a re-renderAn exception to the above rule is updating the state based on some DOM property which can be only computed once a component has re-rendered (e.g. position / dimensions of some DOM nodes)….

React provides developers with many methods or “hooks” that are called during the life-cycle of an component, which allows us to update the UI and application state. Knowing when to use which of them…
Continue reading “Understanding React — Component life-cycle – Bartosz Szczeciński – Medium”

Understanding React — Component life-cycle – Bartosz Szczeciński – Medium

Understanding React — Component life-cycle

☞ 

#reactjs #JavaScript

  • In all other instances remember to use this.setState – DO – set initial stateif not using class properties syntax — prepare all class fields and bind functions that will be passed as callbacksDON’T – cause any side effects (AJAX calls etc.)componentWillMountThis is a somehow special case — componentWillMount does not differ much from constructor…
  • DO – update state via this.setStateperform last minute optimizationcause side-effects (AJAX calls etc.) in case of server-side-rendering onlyDON’T – cause any side effects (AJAX calls etc.) on client function will be called in each update life-cycle caused by changes to props (parent component re-rendering) and will be passed an object…
  • DO – use for increasing performance of poor performing ComponentsDON’T – cause any side effects (AJAX calls etc.)call nextState)If the shouldComponentUpdate function is not implemented, or it decided that the component should update in this render cycle, another life-cycle function will be called.
  • == this.props.myProp) { – // this.props.myProp has a different value – // we can perform any operations that would – // need the new value and/or cause side-effects – // like AJAX calls with the new value – this.props.myProp – } – }DO – cause side effects (AJAX calls etc.)DON’T…
  • DO – cause side effects (AJAX calls etc.)DON’T – call this.setState as it will result in a re-renderAn exception to the above rule is updating the state based on some DOM property which can be only computed once a component has re-rendered (e.g. position / dimensions of some DOM nodes)….

React provides developers with many methods or “hooks” that are called during the life-cycle of an component, which allows us to update the UI and application state. Knowing when to use which of them…
Continue reading “Understanding React — Component life-cycle – Bartosz Szczeciński – Medium”

React State From the Ground Up

#ReactJS State From the Ground Up #JavaScript

  • State, in React, is a plain JavaScript object that allows you keep track of a component’s data.
  • The initial state of the App component has been set to a state object which contains the key username, and its value using .
  • Initializing a component state can get as complex as what you can see here: – – An initialized state can be accessed in the method, as I did above.
  • Your component should look like this; – – A state can be passed as props from a parent to the child component.
  • This method will be used to update the state of the component.

As you begin to learn React, you will be faced with understanding what state is. State is hugely important in React, and perhaps a big reason you’ve looked into using React in the first place. Let’s take a stab at understanding what state is and how it works. What is State? State, in React, is a plain JavaScript
Continue reading “React State From the Ground Up”

React Tutorial: A Comprehensive Guide to learning React.js in 2018

  • These components are defined either in pure JavaScript or they can be defined in what the React team calls “JSX”.
  • The reason the React team went with this approach is because, since the virtual DOM is a JavaScript representation of the actual DOM, React can keep track of the difference between the current virtual DOM(computed after some data changes), with the previous virtual DOM (computed befores some data changes).
  • In more layman’s terms, because manipulating the actual DOM is slow, React is able to minimize manipulations to the actual DOM by keeping track of a virtual DOM and only updating the real DOM when necessary and with only the necessary changes.
  • The process looks something like this, – – Some user event which changes the state of your app → Re-render virtual DOM -> Diff previous virtual DOM with new virtual DOM -> Only update real DOM with necessary changes.
  • Signal to notify our app some data has changed→ Re-render virtual DOM -> Diff previous virtual DOM with new virtual DOM -> Only update real DOM with necessary changes.

Continue reading “React Tutorial: A Comprehensive Guide to learning React.js in 2018”

A Comprehensive Guide to React.js in 2018

  • These components are defined either in pure JavaScript or they can be defined in what the React team calls “JSX”.
  • The reason the React team went with this approach is because, since the virtual DOM is a JavaScript representation of the actual DOM, React can keep track of the difference between the current virtual DOM(computed after some data changes), with the previous virtual DOM (computed befores some data changes).
  • In more layman’s terms, because manipulating the actual DOM is slow, React is able to minimize manipulations to the actual DOM by keeping track of a virtual DOM and only updating the real DOM when necessary and with only the necessary changes.
  • The process looks something like this, – – Some user event which changes the state of your app → Re-render virtual DOM -> Diff previous virtual DOM with new virtual DOM -> Only update real DOM with necessary changes.
  • Signal to notify our app some data has changed→ Re-render virtual DOM -> Diff previous virtual DOM with new virtual DOM -> Only update real DOM with necessary changes.

This is the original guide for learning to build apps with React.js. Recently upgraded to support React 16.3 and friends.
Continue reading “A Comprehensive Guide to React.js in 2018”

til/mapping-over-one-or-many-children.md at master · jbranchaud/til · GitHub

Mapping over one or more children in #Reactjs

  • In Dynamically Add Props To A Child Component, I talked about how a child element can be reconstituted with additional props.
  • The approach I showed will only work in the case of a single child being nested in that component.
  • What if you want your component to account for one, many, or even children?
  • React comes with a built-in function for mapping that handles these cases.
  • The function allows mapping over one or many elements and if is or , it will return or respectively.

GitHub is where people build software. More than 27 million people use GitHub to discover, fork, and contribute to over 80 million projects.
Continue reading “til/mapping-over-one-or-many-children.md at master · jbranchaud/til · GitHub”

React Tutorial: A Comprehensive Guide to learning React.js in 2018

  • These components are defined either in pure JavaScript or they can be defined in what the React team calls “JSX”.
  • The reason the React team went with this approach is because, since the virtual DOM is a JavaScript representation of the actual DOM, React can keep track of the difference between the current virtual DOM(computed after some data changes), with the previous virtual DOM (computed befores some data changes).
  • In more layman’s terms, because manipulating the actual DOM is slow, React is able to minimize manipulations to the actual DOM by keeping track of a virtual DOM and only updating the real DOM when necessary and with only the necessary changes.
  • The process looks something like this, – – Some user event which changes the state of your app → Re-render virtual DOM -> Diff previous virtual DOM with new virtual DOM -> Only update real DOM with necessary changes.
  • Signal to notify our app some data has changed→ Re-render virtual DOM -> Diff previous virtual DOM with new virtual DOM -> Only update real DOM with necessary changes.

Continue reading “React Tutorial: A Comprehensive Guide to learning React.js in 2018”

Making ReactJS Realtime With Websockets

Making #ReactJS Realtime With #Websockets

  • Installation – Now, install create-react-app and also scaffold a new React app with the following commands: – npm install -g create-react-app – – create-react-app react-pusher – – Once all the necessary files are installed, change directory into react-“pusher and start the application with: – npm start – – By now,…
  • There are number of dependencies required for the application server, so let’s install them immediately: – npm install –save axios body-parser cors express pusher pusher-js – – To configure the entry point of the application, create a file called server.js and paste the code below into it: – const Pusher…
  • /ChatBox.css’; – export default ({ text, username, handleTextChange }) = ( – div – div className=”row” – div className=”col-xs-12″ – div className=”chat” – div className=”col-xs-5 col-xs-offset-3″ – input – type=”text” – value={text} – placeholder=”chat here…” – className=”form-control” – onChange={handleTextChange} – onKeyDown={handleTextChange} – / – /div – div className=”clearfix”/div – /div…
  • /avatar.png”; – export default ({ chats }) = ( – ul – {chats.map(chat = { – return ( – div – div className=”row show-grid” – div className=”col-xs-12″ – – div className=”chatMessage” – div key={chat.id} className=”box” – p – strong{chat.username}/strong – /p – p{chat.message}/p – /div – div className=”imageHolder” – img…
  • The state variables in the app are created and defined in the constructor like this: – … – class App extends Component { – constructor(props) { – super(props); – this.state = { – text: ”, – username: ”, – chats: [] – }; – } – componentDidMount() { – ……

This quick tutorial will lead you through building a basic, realtime group chat app, similar to our demo here…
Continue reading “Making ReactJS Realtime With Websockets”

Understanding React — Component life-cycle – Bartosz Szczeciński – Medium

Understanding React — Component life-cycle

#react #reactjs #js

  • DOupdate state via this.setStateperform last minute optimizationcause side-effects (AJAX calls etc.) in case of server-side-rendering onlyDON’Tcause any side effects (AJAX calls etc.) on client function will be called in each update life-cycle caused by changes to props (parent component re-rendering) and will be passed an object map of all the…
  • == this.props.myProps) { // nextProps.myProp has a different value than our current prop // so we can perform some calculations based on the new value }}Due to the fact that with React Fiber (post 16 beta) this function might be called multiple times before the renderfunction is actually called it…
  • == this.props.myProp) { // this.props.myProp has a different value // we can perform any operations that would // need the new value and/or cause side-effects // like AJAX calls with the new value – this.props.myProp }}DOcause side effects (AJAX calls etc.)DON’Tcall this.setState as it will result in a re-renderAn exception…
  • Please take extra care to prevent against updating if the value did not in fact change as it might result in a render errorInfo)A new addition in React 16 — this life-cycle method is special in way that it can react to events happening in the child component, specifically to any uncaught…
  • Please take extra care to prevent against updating if the value did not in fact change as it might result in a render loop.componentWillUnmountUse this function to “clean up” after the component if it takes advantage of timers (setTimeout, setInterval), opens sockets or performs any operations we need to close…

React provides developers with many methods or “hooks” that are called during the life-cycle of an component, which allows us to update the UI and application state. Knowing when to use which of them…
Continue reading “Understanding React — Component life-cycle – Bartosz Szczeciński – Medium”

Understanding React — Component life-cycle – Bartosz Szczeciński – Medium

Understanding #ReactJS: Component life-cycle

  • DOupdate state via this.setStateperform last minute optimizationcause side-effects (AJAX calls etc.) in case of server-side-rendering onlyDON’Tcause any side effects (AJAX calls etc.) on client function will be called in each update life-cycle caused by changes to props (parent component re-rendering) and will be passed an object map of all the…
  • == this.props.myProps) { // nextProps.myProp has a different value than our current prop // so we can perform some calculations based on the new value }}Due to the fact that with React Fiber (post 16 beta) this function might be called multiple times before the renderfunction is actually called it…
  • == this.props.myProp) { // this.props.myProp has a different value // we can perform any operations that would // need the new value and/or cause side-effects // like AJAX calls with the new value – this.props.myProp }}DOcause side effects (AJAX calls etc.)DON’Tcall this.setState as it will result in a re-renderAn exception…
  • Please take extra care to prevent against updating if the value did not in fact change as it might result in a render errorInfo)A new addition in React 16 — this life-cycle method is special in way that it can react to events happening in the child component, specifically to any uncaught…
  • Please take extra care to prevent against updating if the value did not in fact change as it might result in a render loop.componentWillUnmountUse this function to “clean up” after the component if it takes advantage of timers (setTimeout, setInterval), opens sockets or performs any operations we need to close…

React provides developers with many methods or “hooks” that are called during the life-cycle of an component, which allows us to update the UI and application state. Knowing when to use which of them…
Continue reading “Understanding React — Component life-cycle – Bartosz Szczeciński – Medium”