Improve JSDoc checks with inline @type

Where empty objects are initially assigned (or merged) the compiler needs to know the final “shape” up front

In editors and IDEs this also helps populate tooltip messages during loops etc

src/govuk/common/index.mjs

@@ -67,6 +67,7 @@ export function mergeConfigs (/* configObject1, configObject2, ...configObjects
    */
   var flattenObject = function (configObject) {
     // Prepare an empty return object
+    /** @type {Object<string, unknown>} */
     var flattenedObject = {}
 
     /**
@@ -103,6 +104,7 @@ export function mergeConfigs (/* configObject1, configObject2, ...configObjects
   }
 
   // Start with an empty object as our base
+  /** @type {Object<string, unknown>} */
   var formattedConfigObject = {}
 
   // Loop through each of the remaining passed objects and push their keys
@@ -140,6 +142,7 @@ export function extractConfigByNamespace (configObject, namespace) {
     throw new Error('Provide a `namespace` of type "string" to filter the `configObject` by.')
   }
 
+  /** @type {Object<string, unknown>} */
   var newObject = {}
 
   for (var key in configObject) {

src/govuk/common/normalise-dataset.mjs

@@ -50,6 +50,7 @@ export function normaliseString (value) {
  * @returns {Object<string, unknown>} Normalised dataset
  */
 export function normaliseDataset (dataset) {
+  /** @type {Object<string, unknown>} */
   var out = {}
 
   for (var key in dataset) {

src/govuk/components/accordion/accordion.mjs

@@ -52,6 +52,7 @@ function Accordion ($module, config) {
     i18n: ACCORDION_TRANSLATIONS
   }
 
+  /** @type {AccordionConfig} */
   this.config = mergeConfigs(
     defaultConfig,
     config || {},

src/govuk/components/button/button.mjs

@@ -27,6 +27,7 @@ function Button ($module, config) {
     preventDoubleClick: false
   }
 
+  /** @type {ButtonConfig} */
   this.config = mergeConfigs(
     defaultConfig,
     config || {},

src/govuk/components/character-count/character-count.mjs

@@ -88,6 +88,7 @@ function CharacterCount ($module, config) {
     }
   }
 
+  /** @type {CharacterCountConfig} */
   this.config = mergeConfigs(
     defaultConfig,
     config || {},

src/govuk/components/checkboxes/checkboxes.mjs

@@ -122,6 +122,7 @@ Checkboxes.prototype.syncConditionalRevealWithInputState = function ($input) {
 Checkboxes.prototype.unCheckAllInputsExcept = function ($input) {
   var $component = this
 
+  /** @type {NodeListOf<HTMLInputElement>} */
   var allInputsWithSameName = document.querySelectorAll(
     'input[type="checkbox"][name="' + $input.name + '"]'
   )
@@ -147,6 +148,7 @@ Checkboxes.prototype.unCheckAllInputsExcept = function ($input) {
 Checkboxes.prototype.unCheckExclusiveInputs = function ($input) {
   var $component = this
 
+  /** @type {NodeListOf<HTMLInputElement>} */
   var allInputsWithSameNameAndExclusiveBehaviour = document.querySelectorAll(
     'input[data-behaviour="exclusive"][type="checkbox"][name="' + $input.name + '"]'
   )

src/govuk/components/error-summary/error-summary.mjs

@@ -35,6 +35,7 @@ function ErrorSummary ($module, config) {
     disableAutoFocus: false
   }
 
+  /** @type {ErrorSummaryConfig} */
   this.config = mergeConfigs(
     defaultConfig,
     config || {},

src/govuk/components/notification-banner/notification-banner.mjs

@@ -20,6 +20,7 @@ function NotificationBanner ($module, config) {
     disableAutoFocus: false
   }
 
+  /** @type {NotificationBannerConfig} */
   this.config = mergeConfigs(
     defaultConfig,
     config || {},

src/govuk/i18n.mjs

@@ -70,6 +70,7 @@ I18n.prototype.t = function (lookupKey, options) {
  * @returns {string} The translation string to output, with ${} placeholders replaced
  */
 I18n.prototype.replacePlaceholders = function (translationString, options) {
+  /** @type {Intl.NumberFormat | undefined} */
   var formatter
 
   if (this.hasIntlNumberFormatSupport()) {