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One of the most frequently overlooked principles of creating interactive UIs is transitions. Fortunately, over the last few years, React.js and other component-focused frameworks have changed the way we think about UIs and how we build them.

React Transition Group allows us to transition these components in and out of the DOM in a declarative and efficient way. In this article, we’ll concentrate on the CSSTransition and TransitionGroup components of React Transition Group using simple examples.

Prerequisites

Before we go any further, this article assumes the following:

Node.js ≥v6 is installed on your machine

npm is installed on your machine

You have a basic understanding of React.js

Getting started

To install, run these commands in the terminal:

# npm npm install react-transition-group --save # yarn yarn add react-transition-group

Transition a React component using CSS with CSSTransition

The CSSTransition component allows us to apply transitions to elements entering and leaving the DOM. We can achieve this by using the following props:

in : a Boolean value used to control the appearance of the element

: a Boolean value used to control the appearance of the element timeout : indicates the number of milliseconds it will take to enter or leave the DOM

: indicates the number of milliseconds it will take to enter or leave the DOM unmountOnExit : indicates that when the element disappears, it’s actually going to leave the DOM completely. Below is a code snippet of what it looks like:

<CSSTransition in={this.state.example} timeout={500} classNames='example' unmountOnExit >

Simple list example

Below is our first example on how to use React Transition Group’s CSSTransition :

Before CSSTransition

CSSTransition component (before transition) CSSTransition component (before transition) by Ekwuno using classnames, react, react-dom, react-scripts, react-transition-group

After CSSTransition

CSSTransition component (with transition) CSSTransition component (with transition) by Ekwuno using classnames, react, react-dom, react-scripts, react-transition-group

How the transition was created using CSSTransition

In the first code example, we had a normal component with no transition. This rendered an ordered list as soon as the list button was clicked, with no delay and no extra CSS styling.

But when we decide to give a little more life to this example, we install the react-transition-group while using the <CSSTransition> tag, and pass the information in this.state.showList as props to in , which enables us to add some transitions using CSS.

The timeout props allows us to apply a transition as the list leaves the DOM. We then head over to style.css to add some styles for the transition. CSSTransition gives us four key classNames to use for elements entering and leaving: enter , enter-active , exit , and exit-active .

/* This fires as soon as the element enters the DOM */ .list-transition-enter{ } /* This is where we can add the transition*/ .list-transition-enter-active{ } /* This fires as soon as the this.state.showList is false */ .list-transition-exit{ } /* fires as element leaves the DOM*/ .list-transition-exit-active{ }

Then, in these CSS classes, we can add some awesome (yet simple) CSS in the classes to make it look like the child component grows out of the button.

/* This fires as soon as the element enters the DOM*/ .list-transition-enter { /*We give the list the initial dimension of the list button*/ top: 0; width: 120px; max-height: 40px; color: transparent; background-color: #5a564c; } /* This is where we can add the transition*/ .list-transition-enter-active { top: 45px; width: 200px; max-height: 200px; background-color: #9e8949; transition: all 400ms; } /* This fires as soon as the this.state.showList is false */ .list-transition-exit { top: 45px; width: 200px; max-height: 200px; background-color: #9e8949; } /* fires as element leaves the DOM*/ .list-transition-exit-active { top: 0; width: 120px; max-height: 40px; color: transparent; background-color: #5a564c; transition: all 400ms; }

Note that in the code demo above, you will notice list-transition-enter and list-transition-exit-active have the same values because they are the starting and ending states of the components. However, the transitions only occur when the className is active.

Adding the appear prop to display transition on load

The initial state of the list is set to false. But what if we wanted it to display as the page is mounted to the DOM? We can achieve this by just changing the state of showList to true, but then the transition does not display using the appear prop as shown below:

<CSSTransition in={this.state.showList} timeout={400} classNames="list-transition" unmountOnExit appear >

In the CSS file, the classNames styling for .list-transition-appear would be the same as .list-transition-enter and .list-transition-exit-active since it occurs when the component is mounted, and its only function is to allow the transition to show as it appears.

.list-transition-enter, .list-transition-appear { /*We give the list the initial dimension of the list button*/ top: 0; width: 120px; max-height: 40px; color: transparent; background-color: #5a564c; } /* This is where we can add the transition*/ .list-transition-enter-active, .list-transition-appear-active { top: 45px; width: 200px; max-height: 200px; background-color: #9e8949; transition: all 400ms; }

Using enter and exit props

Sometimes, if the application requires the transition to be disabled in some part of the component’s transition lifecycle, we can do this in the component without editing the CSS or disabling the classNames . We do this using the enter and exit props like so:

<CSSTransition in={this.state.showList} timeout={400} classNames="list-transition" unmountOnExit appear enter = {false} >

This stops the .list-transition-active and .list-transition-enter classes from working.

<CSSTransition in={this.state.showList} timeout={400} classNames="list-transition" unmountOnExit appear exit = {false} >

More lifecycle props in CSSTransition groups

We can use lifecycle props to target specific times in transition phases. These lifecycles do exactly what their names imply:

onEnter : fires when the button is clicked and the operation is engaged

: fires when the button is clicked and the operation is engaged onEntering : fires when the information is entering the DOM

: fires when the information is entering the DOM onEntered : shows that the information has entered the DOM

: shows that the information has entered the DOM onExit : essentially fires when the operation for the element exit is initiated

: essentially fires when the operation for the element exit is initiated onExiting : fires when the information is exiting the DOM

: fires when the information is exiting the DOM onExited : shows that the information has left the DOM

Let’s say we need to highlight the most important activity I like to do. We can highlight the color once the list is rendered and add a delay transition before the highlight. Then, our CSSTransition component becomes:

<CSSTransition in={this.state.showList} timeout={400} classNames="list-transition" unmountOnExit appear onEntered= {this.listSwitch} onExit={this.listSwitch} >

The this.listSwitch state is used to set a conditional class to the hobby we want to highlight. So when highlightedHobby is true , we’re going to get this active variant of list item:

<li className={cx('list-item', { 'list-item--active': this.state .highlightedHobby, })} >Writing JavaScript</li>

The conditional className looks like so:

.list-item--active{ color: blue; transition: 500ms; }

When it opens, we see Writing JavaScript turn blue after a delay of 500ms , which is 100ms later than the transition of the list-item , and it goes back onExit . Since this occurs so fast, we can’t see it leave; but if you inspect the element using developer tools, you’ll notice it.

Applying Transitions to elements in a list using TransitionGroup and CSSTransition

Using this code example, I will explain its use in creating interesting transitions.

List-Example List-Example by Ekwuno using classnames, react, react-dom, react-jss, react-router-dom, react-scripts, react-transition-group, styled-components, styled-transition-group

From the code example, we can see that TransitionGroup maps over the favorite music array and returns each one with a CSSTransition component.

<TransitionGroup component="ul"> {this.state.favorites.map( ({ id, name }) => ( <CSSTransition timeout={500} classNames="fade" key={id} > <li className="favorite">{name}</li> </CSSTransition> ) )} </TransitionGroup>

From the above code example, we can see that the TransitionGroup component renders a component, and we can set this to render anything. It could be UL , div , p , option , etc. But when we do not want to render any component, we can set this to {null} :

<TransitionGroup component={null}>

Transitions using JSS

We have been using Vanilla CSS to implement our CSS transitions; now, we will refactor our CSS to become JavaScript objects. We will start by creating a styles.js file and turning our styles in objects, like so:

// Here we will turn all our Css into JavaScript Objects const startTransitionStyles = { top: 0, width: '120px', maxHeight: '40px', color: 'transparent', backgroundColor: '#5a564c', }; const finishTransitionStyles = { top: '45px', width: '200px', maxHeight: '200px', backgroundColor: '#9e8949', }; const styles = { container: { position: 'relative', }, display: { position: 'relative', zindex: '1', width: '120px', height: '40px', backgroundColor: '#5a564c', border: 'none', borderRadius: '5px', outline: 'none', cursor: 'pointer', transition: 'backgroundColor 350ms', }, displayActive: { backgroundColor: '#000000', }, listBody: { position: 'absolute', top: '45px', Zindex: '1', boxSizing: 'border-box', width: '200px', padding: '0 20px', overflow: 'hidden', backgroundColor: '#9e8949', borderRadius: '5px', }, list: { padding: '0', listStyleType: 'none', }, listItem: { padding: '5px 0', }, listItemActive: { color: 'blue', transition: 'color 500ms', }, listTransitionEnter: { ...startTransitionStyles, }, listTransitionEnterActive: { ...finishTransitionStyles, transition: 'all 400ms', }, listTransitionExit: { ...finishTransitionStyles, }, listTransitionExitActive: { ...startTransitionStyles, transition: 'all 400ms', }, }; export default styles;

The above code snippet is then imported into our refactor.js as:

import styles from './styles';

The implementation of the styles are done using InjectSheet imported from react-jss :

import injectSheet from 'react-jss';

This gives us the classes props, which we can use to access the styling in style.js , like so:

render() { const { classes } = this.props; return ( <div className={classes.container}> <button className={classes.display} onClick={this.switch} > Obinna </button> <CSSTransition in={this.state.showList} timeout={400} classNames="list-transition" unmountOnExit classNames={{ enter: classes.listTransitionEnter, enterActive: classes.listTransitionEnterActive, exit: classes.listTransitionExit, exitActive: classes.listTransitionExitActive, }} > <div className={classes.listBody}> <ul className={classes.list}> <li className={classes.listItem}> Writing JavaScript </li> <li className={classes.listItem}> Running </li> <li className={classes.listItem}> Technical Writing </li> <li className={classes.listItem}> Writing Clean code </li> </ul> </div> </CSSTransition> </div> );

Note that we use classNames here as opposed to className so we can supply multiple classNames .

The transitions are added by passing an object with enter , enter-active , exit , and enter-active keys, and they’ll refer to JSS class names.

<CSSTransition in={this.state.showList} timeout={400} classNames="list-transition" unmountOnExit classNames={{ enter: classes.listTransitionEnter, enterActive:classes.listTransitionEnterActive, exit: classes.listTransitionExit, exitActive:classes.listTransitionExitActive, }} >

CSSTransition component (using JSS) CSSTransition component (using JSS) by Ekwuno using classnames, react, react-dom, react-jss, react-router-dom, react-scripts, react-transition-group, styled-components, styled-transition-group

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Conclusion

Smooth transitions make your application’s user experience more dynamic and welcoming to the end user. React Transition Group helps us achieve this with fewer lines of code that are easier to understand. Happy coding!