Fix radios component with defaultChecked inputs and conditional content

CHANGELOG.md

@@ -1,5 +1,15 @@
 # NHS.UK React components
 
+## Unreleased
+
+This is a bug fix release.
+
+Note: Form components with missing `id` (or `idPrefix`) now fall back to the `name` prop before generating IDs. This helps prevent [hydration mismatch](https://react.dev/link/hydration-mismatch) errors with server-side rendered (SSR) HTML.
+
+### :wrench: **Fixes**
+
+- [#377: Fix radios component with `defaultChecked` inputs and conditional content](https://github.com/NHSDigital/nhsuk-react-components/pull/377)
+
 ## 6.0.0 - 10 March 2026
 
 This version provides support for NHS.UK frontend v10.3.0

src/components/form-elements/character-count/CharacterCount.tsx

@@ -64,7 +64,7 @@ export const CharacterCount = forwardRef<HTMLTextAreaElement, CharacterCountProp
         }}
         {...rest}
       >
-        {({ className, id, error, 'aria-describedby': ariaDescribedBy, ...rest }) => (
+        {({ className, id, error, 'aria-describedby': ariaDescribedBy, ...restRenderProps }) => (
           <>
             <textarea
               className={classNames(
@@ -76,7 +76,7 @@ export const CharacterCount = forwardRef<HTMLTextAreaElement, CharacterCountProp
               id={id}
               aria-describedby={ariaDescribedBy ? `${id}-info ${ariaDescribedBy}` : `${id}-info`}
               ref={forwardedRef}
-              {...rest}
+              {...restRenderProps}
             />
             <div className="nhsuk-hint nhsuk-character-count__message" id={`${id}-info`}>
               {maxWords

src/components/form-elements/checkboxes/Checkboxes.tsx

@@ -3,6 +3,7 @@
 import classNames from 'classnames';
 import { type Checkboxes as CheckboxesModule } from 'nhsuk-frontend';
 import {
+  type ChangeEvent,
   type ComponentPropsWithoutRef,
   forwardRef,
   useEffect,
@@ -27,7 +28,7 @@ export type CheckboxesProps = CheckboxesElementProps &
   Omit<FormElementProps, 'label' | 'labelProps'>;
 
 const CheckboxesComponent = forwardRef<HTMLDivElement, CheckboxesProps>((props, forwardedRef) => {
-  const { children, idPrefix, ...rest } = props;
+  const { children, idPrefix = props.name, onChange, ...rest } = props;
 
   const moduleRef = useRef<HTMLDivElement>(null);
   const importRef = useRef<Promise<CheckboxesModule | void>>(null);
@@ -79,6 +80,12 @@ const CheckboxesComponent = forwardRef<HTMLDivElement, CheckboxesProps>((props,
     _boxIds = {};
   };
 
+  const handleChange = (e: ChangeEvent<HTMLInputElement>) => {
+    if (onChange) {
+      onChange(e);
+    }
+  };
+
   if (instanceError) {
     throw instanceError;
   }
@@ -92,6 +99,7 @@ const CheckboxesComponent = forwardRef<HTMLDivElement, CheckboxesProps>((props,
           getBoxId: (reference) => getBoxId(id, reference),
           leaseReference,
           unleaseReference,
+          handleChange,
         };
         return (
           <div
@@ -101,7 +109,7 @@ const CheckboxesComponent = forwardRef<HTMLDivElement, CheckboxesProps>((props,
               className,
             )}
             data-module="nhsuk-checkboxes"
-            id={id}
+            id={id === rest.id ? id : undefined}
             ref={moduleRef}
             {...restRenderProps}
           >

src/components/form-elements/checkboxes/CheckboxesContext.ts

@@ -1,17 +1,19 @@
 'use client';
 
-import { createContext } from 'react';
+import { type ChangeEvent, createContext } from 'react';
 
 export interface ICheckboxesContext {
   name: string;
   getBoxId: (reference: string) => string | undefined;
   leaseReference: () => string;
   unleaseReference: (reference: string) => void;
+  handleChange: (event: ChangeEvent<HTMLInputElement>) => void;
 }
 
 export const CheckboxesContext = createContext<ICheckboxesContext>({
   name: '',
   getBoxId: () => undefined,
   leaseReference: () => '',
   unleaseReference: () => {},
+  handleChange: () => {},
 });

src/components/form-elements/checkboxes/__tests__/Checkboxes.test.tsx

@@ -194,6 +194,42 @@ describe('Checkboxes', () => {
     expect(fieldRef.current).toHaveClass('nhsuk-checkboxes__input');
   });
 
+  it('does not render the conditional content if not checked', async () => {
+    const { container } = await renderClient(
+      <Checkboxes id="example" name="example">
+        <Checkboxes.Item value="email" conditional={<p className="conditional-test">Test</p>}>
+          Email
+        </Checkboxes.Item>
+        <Checkboxes.Item value="phone">Phone</Checkboxes.Item>
+        <Checkboxes.Item value="text">Text message</Checkboxes.Item>
+      </Checkboxes>,
+      { moduleName: 'nhsuk-checkboxes' },
+    );
+
+    const conditionalElement = container.querySelector('.conditional-test');
+    expect(conditionalElement?.parentElement).toHaveClass('nhsuk-checkboxes__conditional--hidden');
+  });
+
+  it('renders the conditional content if checked', async () => {
+    const { container } = await renderClient(
+      <Checkboxes id="example" name="example">
+        <Checkboxes.Item
+          value="email"
+          conditional={<p className="conditional-test">Test</p>}
+          checked
+        >
+          Email
+        </Checkboxes.Item>
+        <Checkboxes.Item value="phone">Phone</Checkboxes.Item>
+        <Checkboxes.Item value="text">Text message</Checkboxes.Item>
+      </Checkboxes>,
+      { moduleName: 'nhsuk-checkboxes' },
+    );
+
+    const conditionalElement = container.querySelector('.conditional-test');
+    expect(conditionalElement).toHaveTextContent('Test');
+  });
+
   it('sets attribute `data-checkbox-exclusive` when items are exclusive', async () => {
     const { container } = await renderClient(
       <Checkboxes id="example" name="example">

src/components/form-elements/checkboxes/components/CheckboxesItem.tsx

@@ -2,6 +2,7 @@
 
 import classNames from 'classnames';
 import {
+  type ChangeEvent,
   type ComponentPropsWithRef,
   type ComponentPropsWithoutRef,
   type ReactNode,
@@ -31,27 +32,39 @@ export type CheckboxesItemProps = CheckboxesItemElementProps &
 export const CheckboxesItem = forwardRef<HTMLInputElement, CheckboxesItemProps>(
   (props, forwardedRef) => {
     const {
-      id,
-      labelProps,
+      className,
       children,
+      id,
       hint,
       hintProps,
+      labelProps,
       conditional,
-      defaultChecked,
-      checked,
-      forceShowConditional,
       conditionalProps,
+      forceShowConditional,
+      checked,
+      defaultChecked,
       exclusive,
       exclusiveGroup,
+      onChange,
       ...rest
     } = props;
 
-    const { getBoxId, name, leaseReference, unleaseReference } =
-      useContext<ICheckboxesContext>(CheckboxesContext);
+    const {
+      name,
+      getBoxId,
+      leaseReference,
+      unleaseReference,
+      handleChange: ctxHandleChange,
+    } = useContext<ICheckboxesContext>(CheckboxesContext);
 
     const [checkboxReference] = useState<string>(leaseReference());
     const inputID = id || getBoxId(checkboxReference);
-    const shouldShowConditional = !!(checked || defaultChecked);
+
+    const isChecked =
+      // 1. Checkbox is checked via props
+      !!(checked || defaultChecked) ||
+      // 2. Checkbox should be checked (to show conditional)
+      forceShowConditional;
 
     const { className: labelClassName, ...restLabelProps } = labelProps || {};
     const { className: hintClassName, ...restHintProps } = hintProps || {};
@@ -61,20 +74,29 @@ export const CheckboxesItem = forwardRef<HTMLInputElement, CheckboxesItemProps>(
 
     const inputProps: ComponentPropsWithDataAttributes<'input'> = rest;
 
+    const handleChange = (e: ChangeEvent<HTMLInputElement>) => {
+      if (onChange) {
+        onChange(e);
+      }
+
+      ctxHandleChange(e);
+    };
+
     return (
       <>
         <div className="nhsuk-checkboxes__item">
           <input
-            className="nhsuk-checkboxes__input"
+            className={classNames('nhsuk-checkboxes__input', className)}
             id={inputID}
             name={name}
             type="checkbox"
             checked={checked}
-            defaultChecked={defaultChecked}
+            defaultChecked={defaultChecked ?? (checked === undefined ? isChecked : undefined)}
             data-checkbox-exclusive={exclusive}
             data-checkbox-exclusive-group={exclusiveGroup}
             data-aria-controls={conditional ? `${inputID}--conditional` : undefined}
             aria-describedby={hint ? `${inputID}--hint` : undefined}
+            onChange={handleChange}
             ref={forwardedRef}
             {...inputProps}
           />
@@ -98,11 +120,7 @@ export const CheckboxesItem = forwardRef<HTMLInputElement, CheckboxesItemProps>(
           <div
             className={classNames(
               'nhsuk-checkboxes__conditional',
-              {
-                'nhsuk-checkboxes__conditional--hidden': !(
-                  shouldShowConditional || forceShowConditional
-                ),
-              },
+              { 'nhsuk-checkboxes__conditional--hidden': !isChecked },
               conditionalClassName,
             )}
             id={`${inputID}--conditional`}

src/components/form-elements/date-input/DateInput.tsx

@@ -98,7 +98,7 @@ const DateInputComponent = forwardRef<HTMLDivElement, DateInputProps>(
           return (
             <div
               className={classNames('nhsuk-date-input', className)}
-              id={id}
+              id={id === rest.id ? id : undefined}
               ref={forwardedRef}
               {...restRenderProps}
             >

src/components/form-elements/file-upload/FileUpload.tsx

@@ -60,12 +60,12 @@ export const FileUpload = forwardRef<HTMLInputElement, FileUploadProps>(
           'ref': moduleRef,
         }}
       >
-        {({ width, className, error, autoComplete, ...rest }) => (
+        {({ width, className, error, autoComplete, ...restRenderProps }) => (
           <input
             className={classNames('nhsuk-file-upload__input', className)}
             ref={forwardedRef}
             type="file"
-            {...rest}
+            {...restRenderProps}
           />
         )}
       </FormGroup>

src/components/form-elements/password-input/PasswordInput.tsx

@@ -84,7 +84,7 @@ export const PasswordInput = forwardRef<HTMLInputElement, PasswordInputProps>(
           'ref': moduleRef,
         }}
       >
-        {({ width, className, error, autoComplete, ...rest }) => (
+        {({ width, className, error, autoComplete, ...restRenderProps }) => (
           <input
             className={classNames(
               'nhsuk-input',
@@ -98,7 +98,7 @@ export const PasswordInput = forwardRef<HTMLInputElement, PasswordInputProps>(
             spellCheck="false"
             autoCapitalize="none"
             autoComplete={autoComplete ?? 'current-password'}
-            {...rest}
+            {...restRenderProps}
           />
         )}
         {({ id }) => (

src/components/form-elements/radios/Radios.tsx

@@ -3,6 +3,7 @@
 import classNames from 'classnames';
 import { type Radios as RadiosModule } from 'nhsuk-frontend';
 import {
+  type ChangeEvent,
   type ComponentPropsWithoutRef,
   forwardRef,
   useEffect,
@@ -27,13 +28,12 @@ export interface RadiosElementProps extends ComponentPropsWithoutRef<'div'> {
 export type RadiosProps = RadiosElementProps & Omit<FormElementProps, 'label' | 'labelProps'>;
 
 const RadiosComponent = forwardRef<HTMLDivElement, RadiosProps>((props, forwardedRef) => {
-  const { children, idPrefix, ...rest } = props;
+  const { children, idPrefix = props.name, onChange, ...rest } = props;
 
   const moduleRef = useRef<HTMLDivElement>(null);
   const importRef = useRef<Promise<RadiosModule | void>>(null);
   const [instanceError, setInstanceError] = useState<Error>();
   const [instance, setInstance] = useState<RadiosModule>();
-  const [selectedRadio, setSelectedRadio] = useState<string>();
 
   const _radioReferences: string[] = [];
   let _radioCount = 0;
@@ -76,30 +76,31 @@ const RadiosComponent = forwardRef<HTMLDivElement, RadiosProps>((props, forwarde
     _radioReferences.splice(_radioReferences.indexOf(reference), 1);
   };
 
-  const setSelected = (radioReference: string): void => {
-    setSelectedRadio(radioReference);
-  };
-
   const resetRadioIds = (): void => {
     _radioCount = 0;
     _radioIds = {};
   };
 
+  const handleChange = (e: ChangeEvent<HTMLInputElement>) => {
+    if (onChange) {
+      onChange(e);
+    }
+  };
+
   if (instanceError) {
     throw instanceError;
   }
 
   return (
     <FormGroup<RadiosProps, 'div'> inputType="radios" {...rest}>
-      {({ className, inline, small, name, id, error, ...restRenderProps }) => {
+      {({ className, inline, small, name, id, idPrefix, error, ...restRenderProps }) => {
         resetRadioIds();
         const contextValue: IRadiosContext = {
+          name,
           getRadioId: (reference) => getRadioId(id, reference),
-          selectedRadio: selectedRadio,
-          setSelected: setSelected,
           leaseReference: leaseReference,
           unleaseReference: unleaseReference,
-          name,
+          handleChange,
         };
 
         return (
@@ -113,7 +114,7 @@ const RadiosComponent = forwardRef<HTMLDivElement, RadiosProps>((props, forwarde
               className,
             )}
             data-module="nhsuk-radios"
-            id={id}
+            id={id === rest.id ? id : undefined}
             ref={moduleRef}
             {...restRenderProps}
           >

src/components/form-elements/radios/RadiosContext.ts

@@ -1,21 +1,19 @@
 'use client';
 
-import { createContext } from 'react';
+import { type ChangeEvent, createContext } from 'react';
 
 export interface IRadiosContext {
   name: string;
-  selectedRadio?: string;
   getRadioId: (reference: string) => string;
-  setSelected: (radioRef: string) => void;
   leaseReference: () => string;
   unleaseReference: (reference: string) => void;
+  handleChange: (event: ChangeEvent<HTMLInputElement>) => void;
 }
 
 export const RadiosContext = createContext<IRadiosContext>({
   name: '',
-  selectedRadio: '',
   getRadioId: () => '',
-  setSelected: () => {},
   leaseReference: () => '',
   unleaseReference: () => {},
+  handleChange: () => {},
 });