Change number animations direction based on decrease or increase (#12971)

app/javascript/mastodon/components/animated_number.js

@@ -11,16 +11,33 @@ export default class AnimatedNumber extends React.PureComponent {
     value: PropTypes.number.isRequired,
   };
 
-  willEnter () {
-    return { y: -1 };
+  state = {
+    direction: 1,
+  };
+
+  componentWillReceiveProps (nextProps) {
+    if (nextProps.value > this.props.value) {
+      this.setState({ direction: 1 });
+    } else if (nextProps.value < this.props.value) {
+      this.setState({ direction: -1 });
+    }
   }
 
-  willLeave () {
-    return { y: spring(1, { damping: 35, stiffness: 400 }) };
+  willEnter = () => {
+    const { direction } = this.state;
+
+    return { y: -1 * direction };
+  }
+
+  willLeave = () => {
+    const { direction } = this.state;
+
+    return { y: spring(1 * direction, { damping: 35, stiffness: 400 }) };
   }
 
   render () {
     const { value } = this.props;
+    const { direction } = this.state;
 
     if (reduceMotion) {
       return <FormattedNumber value={value} />;
@@ -37,7 +54,7 @@ export default class AnimatedNumber extends React.PureComponent {
         {items => (
           <span className='animated-number'>
             {items.map(({ key, data, style }) => (
-              <span key={key} style={{ position: style.y > 0 ? 'absolute' : 'static', transform: `translateY(${style.y * 100}%)` }}><FormattedNumber value={data} /></span>
+              <span key={key} style={{ position: (direction * style.y) > 0 ? 'absolute' : 'static', transform: `translateY(${style.y * 100}%)` }}><FormattedNumber value={data} /></span>
             ))}
           </span>
         )}