feat(datepicker): formatting dates for mass-inputs

frontend/src/utils/form/datepicker.js

@@ -112,4 +112,20 @@ export class Datepicker {
     if (!this.datepickerInstance.select || !this._element.value) return;
     this._element.value = dateFormat(this.datepickerInstance.select, FORM_DATE_FORMAT);
   }
+
+  /**
+   * Calls formatElementValue on all datepicker objects registered for a form.
+   * @param {*} formID ID of the form for which all datepicker date values should be formatted
+   */
+  static formatAllFormElementValues(formID) {
+    if (!Datepicker.datepickerCollections) {
+      // no datepicker collections yet (i.e. constructor was never called) => do nothing
+      return;
+    }
+
+    if (Datepicker.datepickerCollections.has(formID)) {
+      const datepickerInstances = Datepicker.datepickerCollections.get(formID);
+      datepickerInstances.forEach(instance => instance.formatElementValue());
+    }
+  }
 }

frontend/src/utils/mass-input/mass-input.js

@@ -1,4 +1,5 @@
 import { Utility } from '../../core/utility';
+import { Datepicker } from '../form/datepicker';
 
 const MASS_INPUT_CELL_SELECTOR = '.massinput__cell';
 const MASS_INPUT_ADD_CELL_SELECTOR = '.massinput__cell--add';
@@ -95,6 +96,9 @@ export class MassInput {
         return false;
       }
 
+      // format any date values before submission
+      Datepicker.formatAllFormElementValues(this._massInputForm.id);
+
       event.preventDefault();
       const requestBody = this._serializeForm(submitButton, enctype);