Don't hardcode analysis preview route in Javascript

js/yoast_seo.js

@@ -215,8 +215,7 @@
     var self = this;
 
     this.$form.ajaxSubmit({
-      // TODO: This endpoint probably shouldn't be static.
-      url: '/yoast_seo/preview',
+      url: this.config.analysis_endpoint,
       data: {
         yoast_seo_preview: {
           path: drupalSettings.path.currentPath,

src/Plugin/Field/FieldWidget/YoastSeoWidget.php

@@ -10,6 +10,7 @@ use Drupal\Core\Field\WidgetBase;
 use Drupal\Core\Form\FormStateInterface;
 use Drupal\Core\Field\FieldDefinitionInterface;
 use Drupal\Core\Plugin\ContainerFactoryPluginInterface;
+use Drupal\Core\Url;
 use Drupal\yoast_seo\SeoManager;
 use Symfony\Component\DependencyInjection\ContainerInterface;
 
@@ -177,6 +178,8 @@ class YoastSeoWidget extends WidgetBase implements ContainerFactoryPluginInterfa
       'base_root' => $base_root,
       // Set up score to indiciator word rules.
       'score_status' => $score_to_status_rules,
+      // Set up our analysis endpoint.
+      'analysis_endpoint' => Url::fromRoute('yoast_seo.entity_preview')->toString(),
     ];
 
     // Set up the names of the text outputs.