Add support for async migrations (#64)

index.ts

@@ -68,7 +68,7 @@ export interface Options {
 /*
 Handler signature for when an extension updates.
 */
-export type Migration<UserOptions extends Options> = (savedOptions: UserOptions, defaults: UserOptions) => void;
+export type Migration<UserOptions extends Options> = (savedOptions: UserOptions, defaults: UserOptions) => Promise<void>;
 
 class OptionsSync<UserOptions extends Options> {
 	public static migrations = {
@@ -235,7 +235,8 @@ class OptionsSync<UserOptions extends Options> {
 		this._log('log', 'Found these stored options', {...options});
 		this._log('info', 'Will run', migrations.length, migrations.length === 1 ? 'migration' : ' migrations');
 		for (const migrate of migrations) {
-			migrate(options, this.defaults);
+			// eslint-disable-next-line no-await-in-loop -- Must be done in order
+			await migrate(options, this.defaults);
 		}
 
 		// Only save to storage if there were any changes

test/index.js

@@ -161,6 +161,12 @@ test.serial('migrations alter the stored options', async t => {
 
 	const storage = new OptionsSync({
 		migrations: [
+			async savedOptions => {
+				await new Promise(resolve => {
+					setTimeout(resolve, 100);
+				});
+				savedOptions.size += 10;
+			},
 			savedOptions => {
 				if (typeof savedOptions.size !== 'undefined') {
 					savedOptions.minSize = savedOptions.size;
@@ -175,7 +181,7 @@ test.serial('migrations alter the stored options', async t => {
 	t.is(chrome.storage.sync.set.callCount, 1);
 	t.deepEqual(chrome.storage.sync.set.firstCall.args[0], {
 		options: compressOptions({
-			minSize: 30,
+			minSize: 40,
 		}),
 	});
 });