fix(loader): add new load hook for new API design;

- Closes #13

.github/workflows/ci.yml

@@ -15,7 +15,7 @@ jobs:
     timeout-minutes: 3
     strategy:
       matrix:
-        nodejs: [12, 14, 16]
+        nodejs: [12, 14, 16.11, 16]
         os: [ubuntu-latest, windows-latest]
     steps:
     - uses: actions/checkout@v2

src/loader.ts

@@ -1,4 +1,4 @@
-import { existsSync } from 'fs';
+import { existsSync, promises as fs } from 'fs';
 import { fileURLToPath, URL } from 'url';
 import * as tsm from './utils.js';
 
@@ -22,7 +22,10 @@ type Resolve = (
 		parentURL?: string;
 	},
 	fallback: Resolve
-) => Promisable<{ url: string }>;
+) => Promisable<{
+	url: string;
+	format?: Format;
+}>;
 
 type Inspect = (
 	url: string,
@@ -36,6 +39,15 @@ type Transform = (
 	fallback: Transform
 ) => Promisable<{ source: Source }>;
 
+type Load = (
+	url: string,
+	context: { format?: Format },
+	fallback: Load
+) => Promisable<{
+	format: Format;
+	source: Source;
+}>;
+
 async function toConfig(): Promise<Config> {
 	let mod = await setup;
 	mod = mod && mod.default || mod;
@@ -101,6 +113,27 @@ export const resolve: Resolve = async function (ident, context, fallback) {
 	return fallback(ident, context, fallback);
 }
 
+export const load: Load = async function (uri, context, fallback) {
+	// note: inline `getFormat`
+	let options = await toOptions(uri);
+	if (options == null) return fallback(uri, context, fallback);
+	let format: Format = options.format === 'cjs' ? 'commonjs' : 'module';
+
+	// TODO: decode SAB/U8 correctly
+	let path = fileURLToPath(uri);
+	let source = await fs.readFile(path);
+
+	// note: inline `transformSource`
+	esbuild = esbuild || await import('esbuild');
+	let result = await esbuild.transform(source.toString(), {
+		...options,
+		sourcefile: path,
+		format: format === 'module' ? 'esm' : 'cjs',
+	});
+
+	return { format, source: result.code };
+}
+
 /** @deprecated */
 export const getFormat: Inspect = async function (uri, context, fallback) {
 	let options = await toOptions(uri);