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-basic: Description of the conceptual model of React

  • The core premise for React is that UIs are simply a projection of data into a different form of data.
  • My actual mental model of this is that they return the next version of state during an “update” pass.
  • Most UIs are some form of lists that then produce multiple different values for each item in the list.
  • We can move the logic of extracting and passing state to a low-level function that we reuse a lot.
  • We can use the same trick we used for state and pass a memoization cache through the composable function.

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 “React-basic: Description of the conceptual model of React”

@modernserf Not quite what you’re asking but you might like this

  • The core premise for React is that UIs are simply a projection of data into a different form of data.
  • My actual mental model of this is that they return the next version of state during an “update” pass.
  • Most UIs are some form of lists that then produce multiple different values for each item in the list.
  • We can move the logic of extracting and passing state to a low-level function that we reuse a lot.
  • We can use the same trick we used for state and pass a memoization cache through the composable function.

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 “@modernserf Not quite what you’re asking but you might like this”

How to Animate the Items of a React Native FlatList

  • Animating EntryTo easily demo our animation we’ll animated to insertion of the list item.
  • When a new item is added to the people array we’ll change the opacity of the row and, via transform, the scale and rotation.
  • First we’ll create a new animated value and, when the component mounts, we’ll change that value from 0 to 1 using Animated.timing.
  • Inside the render function we use the animated value to adjust the opacity and scale (directly, because 0 to 1 is what we’re looking for) and the rotation.
  • We’re now left with some subtle, yet slick, animations for each row item for whenever they’re added or removed.

I was recently asked about animating items in a React Native list — specifically animating the item when added and removed. That’s what we’ll cover today! To accomplish this we’ll use the FlatList…
Continue reading “How to Animate the Items of a React Native FlatList”

@ZackArgyle 1. Start with plain React. 2. Lift state as needed. 3. Still feeling pain? Use Redux/Context/etc.

  • Currently, both components independently keep their values in the local state: – – However, we want these two inputs to be in sync with each other.
  • Since the props of both components are coming from the same parent component, the two inputs will always be in sync.
  • It will handle the change by modifying its own local state, thus re-rendering both inputs with the new values.
  • For example, if we enter 37 into the Celsius input, the state of the component will be: – – If we later edit the Fahrenheit field to be 212, the state of the will be: – – We could have stored the value of both inputs but it turns out…
  • The inputs stay in sync because their values are computed from the same state: – – Try it on CodePen.

Often, several components need to reflect the same changing data. We recommend lifting the shared state up to their closest common ancestor. Let’s see how this works in action.
Continue reading “@ZackArgyle 1. Start with plain React.
2. Lift state as needed.
3. Still feeling pain? Use Redux/Context/etc.”

Simple, Touch-Friendly carousel component for @reactjs #reactjs #react-component

Simple, Touch-Friendly carousel component for @reactjs #reactjs #react-component

  • The basic carousel sample.The Carousel component returns a callback function with the following arguments.
  • and must be passed down to the elements – – But the Carousel component also returns other arguments, like , , , , , – – For the component to work, for example, on mobile devices, set the value to true for touching.
  • Set the value for and place the argument in your jsx template – – When you stop moving your mouse triggers a function which calculates the position of the elements.
  • For example, you want to fetch data or trigger some function when you reach the end of the carousel.
  • The default value for is 0 – – must be passed to the component – – Use the arguments and from the callback.

react-awesome-carousel – Simple, Touch-Friendly carousel component for React.js
Continue reading “Simple, Touch-Friendly carousel component for @reactjs #reactjs #react-component”

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”

The most unknown redux performance trick – Julien De Luca – Medium

  • The most unknown redux performance trickRegarding optimizing redux, there are some well known techniques: memoizing, using reselect for example.But there is one that remains unknown to many, although it’s simple and very efficient: The connect’s areStatesEqual option.When state changes, all connect functions will be called, props mapped from state and…
  • Imagine something like this :Considering action addTodo adds a todo item in the todo reducer, when this action will be called, both connect will then be called and mapStateToProps computed.Using areStatesEqual option, you can tell when not to bother to call mapStateToProps at all.The docs say :[areStatesEqual] (Function): When pure, compares incoming…
  • This function is passed 2 arguments: the previous state, and the next state.
  • You return a boolean telling whether the two states have changed, regarding the state slice you’re interested in, and if the function returns true, mapStateToProps will not even be called.Let’s update our example to use this function :Now, when state.users.all changes, the TodoContainer’s areStatesEqual option will be called, it will return…
  • It makes much more sense when using more complex mapStateToProps.Memoization remains useful when using props in mapStateToProps and methods that return new objects or arrays.Perfs gain can be really impressive only using this simple trick.Enjoy !

Regarding optimizing redux, there are some well known techniques: memoizing, using reselect for example. But there is one that remains unknown to many, although it’s simple and very efficient: The…
Continue reading “The most unknown redux performance trick – Julien De Luca – Medium”

Deep dive into observed Components with React.js and FrintJS

  • Higher-order componentThe API of the observe higher-order component (HoC) is quite simple:import React from ‘react’;import { observe } from ‘frint-react’;function MyComponent(props) { return div…/div;}const ObservedComponent = default ObservedComponent;It receives a function (that we called fn above), where you can generate your props that will be ultimately passed to your target…
  • Generating props synchronouslyThe fn function also gives you access to the FrintJS App’s instance:const ObservedComponent = observe(function (app) { // this will be the `props` in MyComponent return {}; })(MyComponent);Since you have access to your app instance, you can also get values from it, including providers:const ObservedComponent = observe(function (app)…
  • Because they have this dynamic nature, the observe HoC gives you access to parent props as an Observable:const ObservedComponent = observe(function (app, props$) { // …})(MyComponent);In addition to your FrintJS App instance (app), there is a second argument props$, which is props passed down to you from the parent Component…
  • But as your application grows, there will be times, when you need to work with multiple Observables and return a single props stream.This is where a helper function called streamProps shipped with frint-react can come handy.If you are an RxJS ninja, you may skip this part =DThe streamProps function will…
  • In that case, you may want to pass some default props to your target component before new values are generated.The streamProps helper function receives an optional first argument, where you can pass your default props:import { streamProps } from ‘frint-react’;const defaultProps = { foo: ‘n/a’, bar: ‘n/a’, baz: ‘n/a’,};const props$…

Our focus in this article will be about using the observe higher-order component, shipped from frint-react package. To make the most out of this, it is advised that you read these previous articles…
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