Show comment posting errors (#12184)

app/assets/javascripts/initializers/initializeCommentsPage.js.erb

@@ -260,11 +260,16 @@ function handleCommentSubmit(event) {
           activateRunkitTags();
         })
       } else {
+        form.classList.remove('submitting');
+        var responseStatus = response.status;
         response.json().then(function parseError(errorReponse) {
-          form.classList.remove('submitting');
-          showRateLimitModal('made a comment', 'making another comment')
-          return false;
+          if (responseStatus === 429) {
+            showRateLimitModal('made a comment', 'making another comment')
+          } else {
+            showUserAlertModal('Error posting comment', 'Your comment could not be posted due to an error: ' + errorReponse.error, 'OK')
+          }
         });
+        return false;
       }
       return false;
     });

spec/system/comments/user_fills_out_comment_spec.rb

@@ -64,6 +64,24 @@ RSpec.describe "Creating Comment", type: :system, js: true do
     end
   end
 
+  context "when there is an error posting a comment" do
+    let(:unconfigured_twitter_comment) { "{% twitter 733111952256335874 %}" }
+
+    before do
+      stub_request(:post, "https://api.twitter.com/oauth2/token")
+        .to_return(status: 400, body: '{"errors":[{"code":215,"message":"Bad Authentication data."}]}', headers: {})
+    end
+
+    it "displays a error modal" do
+      visit article.path.to_s
+      wait_for_javascript
+
+      fill_in "text-area", with: unconfigured_twitter_comment
+      click_button("Submit")
+      expect(page).to have_text("Error posting comment")
+    end
+  end
+
   context "with Runkit tags" do
     before do
       visit article.path.to_s