feat: TypeScript REPL (#7)

README.md

@@ -5,6 +5,7 @@ Node.js runtime that can instantaneously load TypeScript & ESM, powered by [esbu
 ### Features
 - Transforms TypeScript & ESM → to CJS or ESM (depending on [package type](https://nodejs.org/api/packages.html#type))
 - Supports TS extensions `.cjs` & `.mjs` (`.cts` & `.mts`)
+- TypeScript REPL
 - Supports Node.js v12.20+
 - Handles `node:` import prefixes
 - Hides experimental feature warnings

package.json

@@ -21,6 +21,9 @@
 	"files": [
 		"dist"
 	],
+	"exports": {
+		"./repl": "./dist/repl.js"
+	},
 	"bin": "./dist/cli.js",
 	"scripts": {
 		"build": "pkgroll --target=node12.19 --minify",
@@ -31,6 +34,7 @@
 	},
 	"dependencies": {
 		"@esbuild-kit/cjs-loader": "^2.0.0",
+		"@esbuild-kit/core-utils": "^1.1.0",
 		"@esbuild-kit/esm-loader": "^2.0.0"
 	},
 	"optionalDependencies": {

src/cli.ts

@@ -38,6 +38,9 @@ cli({
 			});
 			return;
 		}
+
+		// Load REPL
+		process.argv.push(require.resolve('./repl'));
 	}
 
 	const args = process.argv.slice(2).filter(

src/repl.ts

@@ -0,0 +1,28 @@
+import repl, { type REPLEval } from 'repl';
+import { transform } from '@esbuild-kit/core-utils';
+import { version } from '../package.json';
+
+// Copied from
+// https://github.com/nodejs/node/blob/v18.2.0/lib/internal/main/repl.js#L37
+console.log(
+	`Welcome to tsx v${version} (Node.js ${process.version}).\n`
+      + 'Type ".help" for more information.',
+);
+
+const nodeRepl = repl.start();
+
+const { eval: defaultEval } = nodeRepl;
+
+const preEval: REPLEval = async function (code, context, filename, callback) {
+	const transformed = await transform(code, '.ts').catch(
+		(error) => {
+			console.log(error.message);
+			return { code: '\n' };
+		},
+	);
+
+	return defaultEval.call(this, transformed.code, context, filename, callback);
+};
+
+// @ts-expect-error overriding read-only property
+nodeRepl.eval = preEval;