Move $heading to AccordionSection

Removes the variables storing the class name. Future refactoring will switch it to be a simple variable in the constructor,
rather than a property on the class, but for now it's necessary so it can be accessed from within `Accordion` during refactoring.

Author: romaricpascal

packages/govuk-frontend/src/govuk/components/accordion/accordion-section.mjs

@@ -62,6 +62,17 @@ export class AccordionSection extends Component {
     })
 
     this.$toggle = createShowHideToggle(this.$toggleIcon, this.$toggleText)
+
+    this.$heading = this.$root.querySelector(
+      '.govuk-accordion__section-heading'
+    )
+
+    if (!this.$heading) {
+      throw new ElementError({
+        component: AccordionSection,
+        identifier: `Section heading (\`.govuk-accordion__section-heading\`)`
+      })
+    }
   }
 }
 

packages/govuk-frontend/src/govuk/components/accordion/accordion.mjs

@@ -14,9 +14,6 @@ const sectionExpandedModifier = 'govuk-accordion__section--expanded'
 /** @private */
 const sectionButtonClass = 'govuk-accordion__section-button'
 
-/** @private */
-const sectionHeadingClass = 'govuk-accordion__section-heading'
-
 /** @private */
 const iconClass = 'govuk-accordion-nav__chevron'
 
@@ -179,16 +176,8 @@ export class Accordion extends ConfigurableComponent {
     // before it gets moved to the `AccordionSection` class
     const $header = section.$header
 
-    const $heading = $header.querySelector(`.${sectionHeadingClass}`)
     const $summary = $header.querySelector(`.${sectionSummaryClass}`)
 
-    if (!$heading) {
-      throw new ElementError({
-        component: Accordion,
-        identifier: `Section heading (\`.${sectionHeadingClass}\`)`
-      })
-    }
-
     // Create a button element that will replace the
     // '.govuk-accordion__section-button' span
     const $button = createElement('button', {
@@ -223,8 +212,8 @@ export class Accordion extends ConfigurableComponent {
 
     $button.appendChild(section.$toggle)
 
-    $heading.removeChild(section.$buttonPlaceholder)
-    $heading.appendChild($button)
+    section.$heading.removeChild(section.$buttonPlaceholder)
+    section.$heading.appendChild($button)
   }
 
   /**