Remove check for session storage support

We don’t do anything different if we detect the browser doesn’t support session storage, so we don’t really care.

We do need to wrap attempts to set *or get* from sessions storage in try blocks because setItem can throw `QuotaExceededError` exceptions [1] and some older browsers will throw other exceptions if session storage isn’t available (disabled, or using private browsing) [2] [3]

However we don’t need to do anything different if exceptions are thrown – we can safely catch those exceptions and swallow them.

[1]: https://html.spec.whatwg.org/multipage/webstorage.html#dom-storage-setitem
[2]: https://developer.mozilla.org/en-US/docs/Web/API/Web_Storage_API/Using_the_Web_Storage_API#feature-detecting_localstorage
[3]: https://gist.github.com/paulirish/5558557

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

@@ -91,9 +91,6 @@ export class Accordion extends GOVUKFrontendComponent {
   /** @private */
   $sections
 
-  /** @private */
-  browserSupportsSessionStorage = false
-
   /**
    * @private
    * @type {HTMLButtonElement | null}
@@ -146,7 +143,6 @@ export class Accordion extends GOVUKFrontendComponent {
     }
 
     this.$sections = $sections
-    this.browserSupportsSessionStorage = helper.checkForSessionStorage()
 
     this.initControls()
     this.initSectionHeaders()
@@ -515,6 +511,22 @@ export class Accordion extends GOVUKFrontendComponent {
     this.$showAllIcon.classList.toggle(this.downChevronIconClass, !expanded)
   }
 
+  /**
+   * Get the identifier for a section
+   *
+   * We need a unique way of identifying each content in the Accordion.
+   * Since an `#id` should be unique and an `id` is required for `aria-`
+   * attributes `id` can be safely used.
+   *
+   * @param {Element} $section - Section element
+   * @returns {string | undefined | null} Identifier for section
+   */
+  getIdentifier($section) {
+    const $button = $section.querySelector(`.${this.sectionButtonClass}`)
+
+    return $button?.getAttribute('aria-controls')
+  }
+
   /**
    * Set the state of the accordions in sessionStorage
    *
@@ -523,19 +535,16 @@ export class Accordion extends GOVUKFrontendComponent {
    * @param {boolean} isExpanded - Whether the section is expanded
    */
   storeState($section, isExpanded) {
-    if (this.browserSupportsSessionStorage && this.config.rememberExpanded) {
-      // We need a unique way of identifying each content in the Accordion.
-      // Since an `#id` should be unique and an `id` is required for `aria-`
-      // attributes `id` can be safely used.
-      const $button = $section.querySelector(`.${this.sectionButtonClass}`)
+    if (!this.config.rememberExpanded) {
+      return
+    }
 
-      if ($button) {
-        const contentId = $button.getAttribute('aria-controls')
+    const id = this.getIdentifier($section)
 
-        if (contentId) {
-          window.sessionStorage.setItem(contentId, isExpanded.toString())
-        }
-      }
+    if (id) {
+      try {
+        window.sessionStorage.setItem(id, isExpanded.toString())
+      } catch (exception) {}
     }
   }
 
@@ -546,19 +555,20 @@ export class Accordion extends GOVUKFrontendComponent {
    * @param {Element} $section - Section element
    */
   setInitialState($section) {
-    if (this.browserSupportsSessionStorage && this.config.rememberExpanded) {
-      const $button = $section.querySelector(`.${this.sectionButtonClass}`)
+    if (!this.config.rememberExpanded) {
+      return
+    }
 
-      if ($button) {
-        const contentId = $button.getAttribute('aria-controls')
-        const contentState = contentId
-          ? window.sessionStorage.getItem(contentId)
-          : null
+    const id = this.getIdentifier($section)
 
-        if (contentState !== null) {
-          this.setExpanded(contentState === 'true', $section)
+    if (id) {
+      try {
+        const state = window.sessionStorage.getItem(id)
+
+        if (state !== null) {
+          this.setExpanded(state === 'true', $section)
         }
-      }
+      } catch (exception) {}
     }
   }
 
@@ -621,27 +631,6 @@ export class Accordion extends GOVUKFrontendComponent {
   })
 }
 
-const helper = {
-  /**
-   * Check for `window.sessionStorage`, and that it actually works.
-   *
-   * @returns {boolean} True if session storage is available
-   */
-  checkForSessionStorage: function () {
-    const testString = 'this is the test string'
-    let result
-    try {
-      window.sessionStorage.setItem(testString, testString)
-      result =
-        window.sessionStorage.getItem(testString) === testString.toString()
-      window.sessionStorage.removeItem(testString)
-      return result
-    } catch (exception) {
-      return false
-    }
-  }
-}
-
 /**
  * Accordion config
  *