add preventable and reversible event helper system

src/lib/index.ts

@@ -31,6 +31,7 @@ export { default as Label } from './Label.svelte';
 export { default as Link, rewriteHref } from './Link.svelte';
 export { default as PhoneInput } from './PhoneInput.svelte';
 export { default as PinInput } from './PinInput.svelte';
+export { type Preventable, checkPreventer, type Reversible, checkReversible } from './prevent';
 export { default as RadioGroup } from './RadioGroup.svelte';
 export { default as ScrollBox } from './ScrollBox.svelte';
 export { default as Spinner } from './Spinner.svelte';

src/lib/prevent.ts

@@ -0,0 +1,63 @@
+/**
+ * A type for a function that can be prevented from executing its default behavior.
+ * See checkPreventer for easy usage of this type.
+ */
+export type Preventable<T> = (ev: T & { prevent: () => void }) => Promise<void> | void;
+
+/**
+ * Calls the provided function with a preventer object, and if the preventer is not
+ * prevented, calls the callback function.
+ * @param fn The function to call with the preventer.
+ * @param ev The event object to pass to the function.
+ * @param cb The callback function to call if the preventer is not prevented.
+ * @returns A promise that resolves to true if the action was not prevented, or false if it was prevented.
+ */
+export const checkPreventer = async <T>(
+	fn: Preventable<T>,
+	ev: T,
+	cb?: () => void
+): Promise<boolean> => {
+	let prevented = false;
+	const preventer = {
+		prevent: () => {
+			prevented = true;
+		}
+	};
+	await fn({ ...ev, ...preventer });
+	if (!prevented && cb) {
+		cb();
+	}
+	return !prevented;
+};
+
+/**
+ * A type for a function that can be reversed after executing its behavior.
+ * See checkReversible for easy usage of this type.
+ */
+export type Reversible<T> = (ev: T & { reverse: () => void }) => Promise<void> | void;
+
+/**
+ * Calls the provided function with a reverser object, and if the reverser is
+ * reversed, calls the callback function.
+ * @param fn The function to call with the reverser.
+ * @param ev The event object to pass to the function.
+ * @param cb The callback function to call if the reverser is reversed.
+ * @returns A promise that resolves to true if the action was not reversed, or false if it was reversed.
+ */
+export const checkReversible = async <T>(
+	fn: Reversible<T>,
+	ev: T,
+	cb?: () => void
+): Promise<boolean> => {
+	let reversed = false;
+	const reverser = {
+		reverse: () => {
+			reversed = true;
+		}
+	};
+	await fn({ ...ev, ...reverser });
+	if (reversed && cb) {
+		cb();
+	}
+	return !reversed;
+};