fix(a11y): fix a11y warning in alert, and other a11y fixes (#3237)

* fix(a11y): fix a11y warning in alert, and other a11y fixes

* chore: correct import

* chore: use `class`

js/src/common/components/Alert.tsx

@@ -3,6 +3,8 @@ import Button from './Button';
 import listItems from '../helpers/listItems';
 import extract from '../utils/extract';
 import type Mithril from 'mithril';
+import classList from '../utils/classList';
+import app from '../app';
 
 export interface AlertAttrs extends ComponentAttrs {
   /** The type of alert this is. Will be used to give the alert a class name of `Alert--{type}`. */
@@ -24,7 +26,7 @@ export default class Alert<T extends AlertAttrs = AlertAttrs> extends Component<
     const attrs = Object.assign({}, this.attrs);
 
     const type = extract(attrs, 'type');
-    attrs.className = 'Alert Alert--' + type + ' ' + (attrs.className || '');
+    attrs.className = classList('Alert', `Alert--${type}`, attrs.className);
 
     const content = extract(attrs, 'content') || vnode.children;
     const controls = (extract(attrs, 'controls') || []) as Mithril.Vnode[];
@@ -37,13 +39,20 @@ export default class Alert<T extends AlertAttrs = AlertAttrs> extends Component<
     const dismissControl: Mithril.Vnode[] = [];
 
     if (dismissible || dismissible === undefined) {
-      dismissControl.push(<Button icon="fas fa-times" className="Button Button--link Button--icon Alert-dismiss" onclick={ondismiss} />);
+      dismissControl.push(
+        <Button
+          aria-label={app.translator.trans('core.lib.alert.dismiss_a11y_label')}
+          icon="fas fa-times"
+          class="Button Button--link Button--icon Alert-dismiss"
+          onclick={ondismiss}
+        />
+      );
     }
 
     return (
       <div {...attrs}>
-        <span className="Alert-body">{content}</span>
-        <ul className="Alert-controls">{listItems(controls.concat(dismissControl))}</ul>
+        <span class="Alert-body">{content}</span>
+        <ul class="Alert-controls">{listItems(controls.concat(dismissControl))}</ul>
       </div>
     );
   }

js/src/common/components/AlertManager.js

@@ -1,5 +1,4 @@
 import Component from '../Component';
-import Alert from './Alert';
 
 /**
  * The `AlertManager` component provides an area in which `Alert` components can
@@ -14,14 +13,18 @@ export default class AlertManager extends Component {
 
   view() {
     return (
-      <div className="AlertManager">
-        {Object.entries(this.state.getActiveAlerts()).map(([key, alert]) => (
-          <div className="AlertManager-alert">
+      <div class="AlertManager">
+        {Object.entries(this.state.getActiveAlerts()).map(([key, alert]) => {
+          const urgent = alert.attrs.type === 'error';
+
+          return (
+            <div class="AlertManager-alert" role="alert" aria-live={urgent ? 'assertive' : 'polite'}>
               <alert.componentClass {...alert.attrs} ondismiss={this.state.dismiss.bind(this.state, key)}>
                 {alert.children}
               </alert.componentClass>
             </div>
-        ))}
+          );
+        })}
       </div>
     );
   }

locale/core.yml

@@ -504,6 +504,10 @@ core:
   lib:
     debug_button: Debug
 
+    # These translations are used in the Alert component.
+    alert:
+      dismiss_a11y_label: Dismiss alert
+
     # These translations are displayed as tooltips for discussion badges.
     badge:
       hidden_tooltip: Hidden