Fire native change events from Input number steppers

Route stepper value changes through the native input setter and dispatch
input/change events so React onChange and DOM listeners see the update.
Read the live DOM value while holding a stepper so repeats don't lag.

src/form/Input/NumberInputButtons.tsx

@@ -9,6 +9,12 @@ type Props = Pick<InputProps<any>, "min" | "max" | "step" | "decimal"> & {
     setValue: React.Dispatch<React.SetStateAction<string>>;
     buttonDownRef: React.MutableRefObject<boolean>;
     inputRef: React.RefObject<HTMLInputElement | null>;
+    /**
+     * Applies the stepped value through the native input setter so that the
+     * `input`/`change` events (React's `onChange`) actually fire. Falls back to
+     * `setValue` when omitted.
+     */
+    applyValue?: (nextValue: string) => void;
 };
 
 /**
@@ -23,6 +29,7 @@ export default function NumberInputButtons({
     buttonDownRef,
     inputRef,
     decimal,
+    applyValue,
 }: Props) {
     const PRESS_TRIGGER_TIMEOUT = 200;
     const PRESS_REPEAT_INTERVAL = 50;
@@ -65,10 +72,15 @@ export default function NumberInputButtons({
 
     const endsWithDecimalPoint = String(value).match(/\.$/);
 
+    /** The DOM value is the freshest source while a press repeats: the native
+     * setter writes it before React re-renders this component. */
+    function currentValue() {
+        const elementValue = inputRef.current?.value;
+        return twuiNumberfy(elementValue ?? value, decimal);
+    }
+
     function applyDelta(delta: number) {
-        setValue((previousValue) => {
+        const nextValue = clamp(currentValue() + delta);
-            const currentValue = twuiNumberfy(previousValue, decimal);
-            const nextValue = clamp(currentValue + delta);
 
         // Round off float drift (e.g. 0.1 + 0.2) before stringifying.
         const roundedValue =
@@ -76,8 +88,14 @@ export default function NumberInputButtons({
                 ? Number(nextValue.toFixed(10))
                 : Number(nextValue.toFixed(decimal));
 
-            return String(roundedValue);
+        const finalValue = String(roundedValue);
-        });
+
+        if (applyValue) {
+            applyValue(finalValue);
+            return;
+        }
+
+        setValue(finalValue);
     }
 
     function stepSize() {

src/form/Input/index.tsx

@@ -286,6 +286,22 @@ export default function Input<KeyType extends string>(
         props.onChange?.(e);
     }
 
+    /** Stepper buttons must behave like typing: write through the native setter
+     * and dispatch `input` (React's `onChange`) plus `change` (native
+     * listeners). React's value tracker sees the value already reported by
+     * `input`, so the `change` dispatch cannot fire `onChange` twice. */
+    function applyStepperValue(nextValue: string) {
+        const element = inputRef?.current;
+
+        if (element) {
+            setNativeInputValue(element, nextValue);
+            element.dispatchEvent(new Event("change", { bubbles: true }));
+            return;
+        }
+
+        setValue(nextValue);
+    }
+
     // function updateValue(
     //     v: string,
     //     el?: HTMLInputElement | HTMLTextAreaElement,
@@ -524,6 +540,7 @@ export default function Input<KeyType extends string>(
                         step={props.step}
                         buttonDownRef={buttonDownRef}
                         decimal={decimal}
+                        applyValue={applyStepperValue}
                     />
                 ) : null}
             </div>