@mmorrissey/react-css-transition-replace

React CSS Transition Replace

A React component to animate replacing one element with another.

While ReactCSSTransitionGroup does a great job of animating changes to a list of components and can even be used to animate the replacement of one item with another, proper handling of the container height in the latter case is not built in. This component is designed to do exactly that with an API closely following that of ReactCSSTransitionGroup.

Using react-css-transition-replace provides two distinct benefits:

• It automatically handles the positioning of the animated components, and
• allows changes in the height of container to be handled and animated with ease when various content heights differ, even when absolute positioning is used.

Animations are fully configurable with CSS, including having the entering component wait to enter until the leaving component's animation completes. Following suit with the React.js API the one caveat is that the transition duration must be specified in JavaScript as well as CSS.

Live Examples | Change Log | Upgrade Guide

Installation

Install via npm:

npm install --save react-css-transition-replace

Usage

A ReactCSSTransitionReplace component can only have a single child. Other than that, the basic usage follows the exact same API as ReactCSSTransitionGroup. When the key of the child component changes, the previous component is animated out and the new component animated in. During this process:

• The leaving component continues to be rendered as usual with static positioning.
• The entering component is positioned on top of the leaving component with absolute positioning.
• The height of the container is set to that of the leaving component, and then immediately to that of the entering component, and the {animation-name}-height class is applied to it.

This provides many possibilities for animating the replacement as illustrated in the examples below.

It is also possible to remove the child component (i.e. leave ReactCSSTransitionReplace with no children) which will animate the height going to zero along with the leave transition. Similarly, a single child can be added to an empty ReactCSSTransitionReplace, triggering the inverse animation.

Cross-fading two components

The ReactCSSTransitionReplace component is used exactly like its ReactCSSTransitionGroup counterpart:

import ReactCSSTransitionReplace from 'react-css-transition-replace';

render() {
  return (
    <ReactCSSTransitionReplace transitionName="cross-fade" 
                               transitionEnterTimeout={1000} transitionLeaveTimeout={1000}>
      <SomeComponent key="uniqueValue"/>
    </ReactCSSTransitionReplace>
  );
}

To realize cross-fading of two components all that remains is to define the enter and leave opacity transitions in the associated CSS classes:

.cross-fade-leave {
  opacity: 1;
}
.cross-fade-leave.cross-fade-leave-active {
  opacity: 0;
  transition: opacity 1s ease-in;
}

.cross-fade-enter {
  opacity: 0;
}
.cross-fade-enter.cross-fade-enter-active {
  opacity: 1;
  transition: opacity 1s ease-in;
}

.cross-fade-height {
  transition: height .5s ease-in-out;
}

Note the additional .cross-fade-height class. This indicates how the container height is to be animated if the heights of the entering and leaving components are not the same. You can see this in action here.

Fade out, then fade in

To fade a component out and wait for its transition to complete before fading in the next, simply add a delay to the enter transition.

.fade-wait-leave {
  opacity: 1;
}
.fade-wait-leave.fade-wait-leave-active {
  opacity: 0;
  transition: opacity .4s ease-in;
}

.fade-wait-enter {
  opacity: 0;
}
.fade-wait-enter.fade-wait-enter-active {
  opacity: 1;
  /* Delay the enter animation until the leave completes */
  transition: opacity .4s ease-in .6s;
}

.fade-wait-height {
  transition: height .6s ease-in-out;
}

Note: The transitionEnterTimeout specified in the JS must be long enough to allow for the delay and the duration of the transition. In this case:

<ReactCSSTransitionReplace transitionName="fade-wait" 
                           transitionEnterTimeout={1000} transitionLeaveTimeout={400}>

See the live example here.

Tips

1. In general animating block or inline-block level elements is more stable that inline elements. If the height changes in random ways ensure that there isn't a span or other inline element used as the outer element of the components being animated.
2. The overflow of the container is set to 'hidden' automatically, which changes the behaviour of collapsing margins from the default 'visible'. This may cause a glitch in the height at the start or end of animations. To avoid this you can:
   • Keep the overflow hidden permanently with custom styles/classes if that will not cause undesired side-effects.
   • Only use Single-direction margin declarations to avoid collapsing margins overall.
   • Turn this feature off by setting the overflowHidden={false} prop when hidden overflow is not needed, for example when transitions are in place and content is of the same height.
3. If the .*-height class is not specified the change in container height will not be animated but instead jump to the height of the entering component instantaneously. It can, therefore, be omitted if all content is known to be of the same height without any adverse side-effects, and absolute positioning related height issues will still be avoided.

Contributing

PRs are welcome.

License

This software is free to use under the MIT license. See the LICENSE file for license text and copyright information.