Add character count Intl.Segmenter support with customisable count function

packages/govuk-frontend/src/govuk/common/configuration.mjs

@@ -79,10 +79,15 @@ export class ConfigurableComponent extends Component {
       normaliseDataset(childConstructor, this._$root.dataset)
     )
 
+    // Override defaults with JavaScript config
+    this._config = /** @type {ConfigurationType} */ (
+      mergeConfigs(childConstructor.defaults, config ?? {})
+    )
+
+    // Override merged config with dataset config
     this._config = /** @type {ConfigurationType} */ (
       mergeConfigs(
-        childConstructor.defaults,
-        config ?? {},
+        this._config,
         this[configOverride](datasetConfig),
         datasetConfig
       )
@@ -107,6 +112,13 @@ export class ConfigurableComponent extends Component {
  * @returns {string | boolean | number | undefined} Normalised data
  */
 export function normaliseString(value, property) {
+  if (
+    property?.type &&
+    !['string', 'number', 'boolean'].includes(property.type)
+  ) {
+    return
+  }
+
   const trimmedValue = value ? value.trim() : ''
 
   let output
@@ -374,7 +386,8 @@ export function extractConfigByNamespace(schema, dataset, namespace) {
 /**
  * @internal
  * @typedef {keyof ObjectNested} NestedKey
- * @typedef {{ [key: string]: string | boolean | number | ObjectNested | undefined }} ObjectNested
+ * @typedef {string | boolean | number} NestedValue
+ * @typedef {{ [key: string]: NestedValue | ((...args: any[]) => NestedValue) | ObjectNested | undefined }} ObjectNested
  */
 
 /**
@@ -390,7 +403,7 @@ export function extractConfigByNamespace(schema, dataset, namespace) {
  * Schema property for component config
  *
  * @typedef {object} SchemaProperty
- * @property {'string' | 'boolean' | 'number' | 'object'} type - Property type
+ * @property {'string' | 'boolean' | 'number' | 'object' | 'function'} type - Property type
  */
 
 /**

packages/govuk-frontend/src/govuk/common/configuration/normalise-dataset.jsdom.test.mjs

@@ -25,7 +25,8 @@ describe('normaliseDataset', () => {
               aStringBoolean: { type: 'string' },
               aStringNumber: { type: 'string' },
               anOptionalString: { type: 'string' },
-              anObject: { type: 'object' }
+              anObject: { type: 'object' },
+              aFunction: { type: 'function' }
             }
           }
         },
@@ -39,7 +40,8 @@ describe('normaliseDataset', () => {
           anOptionalString: '',
           'anObject.one': '111',
           'anObject.two': '222',
-          'anObject.three': '333'
+          'anObject.three': '333',
+          aFunction: '() => "albatross"'
         }
       )
     ).toEqual({
@@ -54,7 +56,8 @@ describe('normaliseDataset', () => {
         one: 111,
         two: 222,
         three: 333
-      }
+      },
+      aFunction: undefined // Functions are not normalised from datasets
     })
   })
 })
@@ -69,6 +72,7 @@ describe('normaliseDataset', () => {
  * @property {string} aStringNumber - A string number
  * @property {string} [anOptionalString] - An optional string
  * @property {{ one: string, two: string, three: string }} anObject - An object
+ * @property {(name: string) => string} aFunction - A function
  */
 
 /**

packages/govuk-frontend/src/govuk/common/configuration/normalise-string.jsdom.test.mjs

@@ -80,4 +80,25 @@ describe('normaliseString', () => {
   it('does not normalise whitespace only strings', () => {
     expect(normaliseString('   ')).toBe('   ')
   })
+
+  it('handles missing property schema', () => {
+    // @ts-expect-error Property 'type' is missing
+    expect(normaliseString('true', {})).toBe(true)
+
+    // @ts-expect-error Property 'type' is missing
+    expect(normaliseString('1337', {})).toBe(1337)
+  })
+
+  it('skips unhandled property schema', () => {
+    const inputFunction = '() => "albatross"'
+    const inputObject = '{ not: "allowed" }'
+
+    // Functions in strings are ignored even with schema property type
+    expect(normaliseString(inputFunction)).toBe(inputFunction)
+    expect(normaliseString(inputFunction, { type: 'function' })).toBeUndefined()
+
+    // Objects in strings are ignored even with schema property type
+    expect(normaliseString(inputObject)).toBe(inputObject)
+    expect(normaliseString(inputObject, { type: 'object' })).toBeUndefined()
+  })
 })