Rename JSX files with proper .jsx extension (#23733)

app/javascript/mastodon/components/column_back_button.jsx

@@ -0,0 +1,54 @@
+import React from 'react';
+import { FormattedMessage } from 'react-intl';
+import PropTypes from 'prop-types';
+import Icon from 'mastodon/components/icon';
+import { createPortal } from 'react-dom';
+
+export default class ColumnBackButton extends React.PureComponent {
+
+  static contextTypes = {
+    router: PropTypes.object,
+  };
+
+  static propTypes = {
+    multiColumn: PropTypes.bool,
+  };
+
+  handleClick = () => {
+    if (window.history && window.history.length === 1) {
+      this.context.router.history.push('/');
+    } else {
+      this.context.router.history.goBack();
+    }
+  };
+
+  render () {
+    const { multiColumn } = this.props;
+
+    const component = (
+      <button onClick={this.handleClick} className='column-back-button'>
+        <Icon id='chevron-left' className='column-back-button__icon' fixedWidth />
+        <FormattedMessage id='column_back_button.label' defaultMessage='Back' />
+      </button>
+    );
+
+    if (multiColumn) {
+      return component;
+    } else {
+      // The portal container and the component may be rendered to the DOM in
+      // the same React render pass, so the container might not be available at
+      // the time `render()` is called.
+      const container = document.getElementById('tabs-bar__portal');
+      if (container === null) {
+        // The container wasn't available, force a re-render so that the
+        // component can eventually be inserted in the container and not scroll
+        // with the rest of the area.
+        this.forceUpdate();
+        return component;
+      } else {
+        return createPortal(component, container);
+      }
+    }
+  }
+
+}