feat(cli): implement a default "loader" for JavaScript files

Supports any of the `.js`, `.cjs` and `.mjs` file extensions

packages/cli/src/plugin-loader-js.ts

@@ -0,0 +1,44 @@
+import { type LoaderPlugin } from '@emigrate/plugin-tools/types';
+
+const loaderJs: LoaderPlugin = {
+  loadableExtensions: ['.js', '.cjs', '.mjs'],
+  async loadMigration(migration) {
+    const migrationModule: unknown = await import(migration.filePath);
+
+    if (typeof migrationModule === 'function') {
+      return async () => {
+        await migrationModule();
+      };
+    }
+
+    if (
+      migrationModule &&
+      typeof migrationModule === 'object' &&
+      'default' in migrationModule &&
+      typeof migrationModule.default === 'function'
+    ) {
+      const migrationFunction = migrationModule.default;
+      return async () => {
+        await migrationFunction();
+      };
+    }
+
+    if (
+      migrationModule &&
+      typeof migrationModule === 'object' &&
+      'up' in migrationModule &&
+      typeof migrationModule.up === 'function'
+    ) {
+      const migrationFunction = migrationModule.up;
+      return async () => {
+        await migrationFunction();
+      };
+    }
+
+    return async () => {
+      throw new Error(`Migration file does not export a function: ${migration.relativeFilePath}`);
+    };
+  },
+};
+
+export default loaderJs;

packages/cli/src/up-command.ts

@@ -4,6 +4,7 @@ import { type LoaderPlugin } from '@emigrate/plugin-tools/types';
 import { ShowUsageError } from './show-usage-error.js';
 import { type Config } from './types.js';
 import { stripLeadingPeriod } from './strip-leading-period.js';
+import pluginLoaderJs from './plugin-loader-js.js';
 
 type ExtraFlags = {
   dry?: boolean;
@@ -40,7 +41,7 @@ export default async function upCommand({ directory, dry, plugins = [] }: Config
   }
 
   const migrationFileExtensions = new Set(migrationFiles.map((file) => stripLeadingPeriod(path.extname(file))));
-  const loaderPlugins = await getOrLoadPlugins('loader', plugins);
+  const loaderPlugins = await getOrLoadPlugins('loader', [...plugins, pluginLoaderJs]);
 
   const loaderByExtension = new Map<string, LoaderPlugin | undefined>(
     [...migrationFileExtensions].map(
@@ -91,10 +92,12 @@ export default async function upCommand({ directory, dry, plugins = [] }: Config
       console.log(' -', name, '...');
 
       const extension = stripLeadingPeriod(path.extname(name));
-      const filename = path.resolve(process.cwd(), directory, name);
+      const cwd = process.cwd();
+      const filePath = path.resolve(cwd, directory, name);
+      const relativeFilePath = path.relative(cwd, filePath);
       const loader = loaderByExtension.get(extension)!;
 
-      const migration = await loader.loadMigration({ name, filename, extension });
+      const migration = await loader.loadMigration({ name, filePath, relativeFilePath, cwd, directory, extension });
 
       try {
         await migration();