date input: add onchange callback prop

src/lib/DateInput.svelte

@@ -24,6 +24,7 @@
 		invalidMessage?: string;
 		class?: ClassValue | undefined | null;
 		format?: FormatString[];
+		onchange?: (date: CalendarDate | null) => void;
 	}
 
 	let {
@@ -37,7 +38,8 @@
 		required = false,
 		invalidMessage = 'Valid date is required',
 		class: classValue,
-		format = ['year', 'month', 'day']
+		format = ['year', 'month', 'day'],
+		onchange
 	}: Props = $props();
 
 	const id = $derived(generateIdentifier('dateinput', name));
@@ -109,6 +111,7 @@
 					setPrevious();
 					previousYearValue = undefined;
 					value = null;
+					onchange?.(value);
 				}
 				return;
 			}
@@ -122,6 +125,7 @@
 					setPrevious();
 					previousMonthValue = undefined;
 					value = null;
+					onchange?.(value);
 				}
 				return;
 			}
@@ -135,6 +139,7 @@
 					setPrevious();
 					previousDayValue = undefined;
 					value = null;
+					onchange?.(value);
 				}
 				return;
 			}
@@ -146,6 +151,7 @@
 			day ?? (value ? value.day : min.day)
 		);
 		value = newDate;
+		onchange?.(value);
 	};
 
 	type caretPos = { start: number; end: number } | null;