From 7d99c07549ba152485eccd1f8cf1da71120c19bb Mon Sep 17 00:00:00 2001
From: Karl Horky <karl.horky@gmail.com>
Date: Mon, 10 Oct 2022 21:21:00 +0200
Subject: [PATCH] feat: add `--esm` option for `ley new` command (#25)

* Add --mjs option to generate ESM migration

* Apply suggestions from code review

* Update index.js

* add `opts.esm` docs to readme

* update typedefs

* add `--esm` mention to ESM docs section

* Update index.js

Co-authored-by: Luke Edwards <luke.edwards05@gmail.com>
---
 index.js  | 18 ++++++++++++------
 ley.d.ts  |  1 +
 readme.md | 24 +++++++++++++++++++++++-
 3 files changed, 36 insertions(+), 7 deletions(-)

diff --git a/index.js b/index.js
index 2305e8e..5ddd746 100644
--- a/index.js
+++ b/index.js
@@ -102,15 +102,21 @@ exports.new = async function (opts={}) {
 	}
 
 	let filename = prefix + '-' + opts.filename.replace(/\s+/g, '-');
-	if (!/\.\w+$/.test(filename)) filename += '.js';
+	if (!/\.\w+$/.test(filename)) filename += opts.esm ? '.mjs' : '.js';
 	let dir = resolve(opts.cwd || '.', opts.dir);
 	let file = join(dir, filename);
 
-	await mkdir(dir).then(() => {
-		let str = 'exports.up = async client => {\n\t// <insert magic here>\n};\n\n';
-		str += 'exports.down = async client => {\n\t// just in case...\n};\n';
-		writeFileSync(file, str);
-	});
+	let str = '';
+	await mkdir(dir);
+	
+	if (opts.mjs) {
+		str += 'export async function up(client) {\n\n}\n\n';
+		str += 'export async function down(client) {\n\n}\n';
+	} else {
+		str += 'exports.up = async client => {\n\n};\n\n';
+		str += 'exports.down = async client => {\n\n};\n';
+	}
+	writeFileSync(file, str);
 
 	return filename;
 }
diff --git a/ley.d.ts b/ley.d.ts
index 0c756d7..2a828dd 100644
--- a/ley.d.ts
+++ b/ley.d.ts
@@ -22,6 +22,7 @@ declare namespace Options {
 		filename: string;
 		timestamp?: boolean;
 		length?: number;
+		esm?: boolean;
 	}
 }
 
diff --git a/readme.md b/readme.md
index 3385945..eb75bf2 100644
--- a/readme.md
+++ b/readme.md
@@ -241,6 +241,20 @@ export async function down(DB) {
 }
 ```
 
+You may generate new migration files in ESM syntax by passing the `--esm` flag to the `ley new` command:
+
+```sh
+$ ley new todos --esm
+#=> migrations/003-todos.mjs
+
+$ cat migrations/003-todos.mjs
+#=> export async function up(client) {
+#=> }
+#=> 
+#=> export async function down(client) {
+#=> }
+```
+
 ## Drivers
 
 Out of the box, `ley` includes drivers for the following npm packages:
@@ -339,7 +353,15 @@ Type: `string`
 
 **Required.** The name of the file to be created.
 
-> **Note:** A prefix will be prepended based on [`opts.timestamp`](#optstimestamp) and [`opts.length`](#optslength) values.<br>The `.js` extension will be applied unless your input already has an extension.
+> **Note:** A prefix will be prepended based on [`opts.timestamp`](#optstimestamp) and [`opts.length`](#optslength) values.<br>If your input does not already end with an extension, then `.js` or `.mjs` will be appended.
+
+#### opts.esm
+Type: `boolean`<br>
+Default: `false`
+
+Create a migration file with ESM syntax.
+
+> **Note:** When true, the `opts.filename` will contain the `.mjs` file extension unless your input already has an extension.
 
 #### opts.timestamp
 Type: `boolean`<br>