Support batch image upload (#2597)

src/composables/useValueTransform.ts

@@ -0,0 +1,31 @@
+/**
+ * Creates a getter/setter pair that transforms values on access if they have changed.
+ * Does not observe deep changes.
+ *
+ * @example
+ * const { get, set } = useValueTransform<ResultItem[], string[]>(
+ *   items => items.map(formatPath)
+ * )
+ *
+ * Object.defineProperty(obj, 'value', { get, set })
+ */
+export function useValueTransform<Internal, External>(
+  transform: (value: Internal) => External,
+  initialValue: Internal
+) {
+  let internalValue: Internal = initialValue
+  let cachedValue: External = transform(initialValue)
+  let isChanged = false
+
+  return {
+    get: () => {
+      if (!isChanged) return cachedValue
+      cachedValue = transform(internalValue)
+      return cachedValue
+    },
+    set: (value: Internal) => {
+      isChanged = true
+      internalValue = value
+    }
+  }
+}