Add support for .mjs config files

fixtures/js-config-file-with-type-module/.size-limit.js

@@ -0,0 +1,5 @@
+export default [
+  {
+    path: 'index.js'
+  }
+]

fixtures/js-config-file-with-type-module/index.js

@@ -0,0 +1,5 @@
+const first = 'first'
+
+const second = 'second'
+
+export { first, second }

fixtures/js-config-file-with-type-module/package.json

@@ -0,0 +1,10 @@
+{
+  "private": true,
+  "name": "js-config-file-with-type-module",
+  "type": "module",
+  "devDependencies": {
+    "@size-limit/webpack": ">= 0.0.0",
+    "@size-limit/webpack-why": ">= 0.0.0",
+    "size-limit": ">= 0.0.0"
+  }
+}

fixtures/js-config-file/.size-limit.js

@@ -0,0 +1,5 @@
+module.exports = [
+  {
+    path: 'index.js'
+  }
+]

fixtures/js-config-file/index.js

@@ -0,0 +1,5 @@
+const first = 'first'
+
+const second = 'second'
+
+export { first, second }

fixtures/js-config-file/package.json

@@ -0,0 +1,9 @@
+{
+  "private": true,
+  "name": "js-config-file",
+  "devDependencies": {
+    "@size-limit/webpack": ">= 0.0.0",
+    "@size-limit/webpack-why": ">= 0.0.0",
+    "size-limit": ">= 0.0.0"
+  }
+}

fixtures/mjs-config-file/.size-limit.mjs

@@ -0,0 +1,5 @@
+export default [
+  {
+    path: 'index.js'
+  }
+]

fixtures/mjs-config-file/index.js

@@ -0,0 +1,5 @@
+const first = 'first'
+
+const second = 'second'
+
+export { first, second }

fixtures/mjs-config-file/package.json

@@ -0,0 +1,9 @@
+{
+  "private": true,
+  "name": "mjs-config-file",
+  "devDependencies": {
+    "@size-limit/webpack": ">= 0.0.0",
+    "@size-limit/webpack-why": ">= 0.0.0",
+    "size-limit": ">= 0.0.0"
+  }
+}

packages/size-limit/get-config.js

@@ -82,6 +82,15 @@ function toName(files, cwd) {
   return files.map(i => (i.startsWith(cwd) ? relative(cwd, i) : i)).join(', ')
 }
 
+/**
+ * Dynamically imports a module from a given file path
+ * and returns its default export.
+ *
+ * @param {string} filePath - The path to the module file to be imported.
+ * @returns {Promise<any>} A promise that resolves with the default export of the module.
+ */
+const dynamicImport = async filePath => (await import(filePath)).default
+
 export default async function getConfig(plugins, process, args, pkg) {
   let config = {
     cwd: process.cwd()
@@ -112,11 +121,16 @@ export default async function getConfig(plugins, process, args, pkg) {
     config.checks = [{ files: args.files }]
   } else {
     let explorer = lilconfig('size-limit', {
+      loaders: {
+        '.js': dynamicImport,
+        '.mjs': dynamicImport
+      },
       searchPlaces: [
         'package.json',
         '.size-limit.json',
         '.size-limit',
         '.size-limit.js',
+        '.size-limit.mjs',
         '.size-limit.cjs'
       ]
     })

packages/size-limit/package.json

@@ -26,7 +26,7 @@
     "bytes-iec": "^3.1.1",
     "chokidar": "^3.5.3",
     "globby": "^14.0.0",
-    "lilconfig": "^3.0.0",
+    "lilconfig": "^3.1.1",
     "nanospinner": "^1.1.0",
     "picocolors": "^1.0.0"
   },

packages/size-limit/test/get-config.test.js

@@ -195,6 +195,48 @@ it('normalizes bundle and webpack arguments with --why and ui-reports', async ()
   })
 })
 
+it('should work with .mjs config file', async () => {
+  expect(await check('mjs-config-file')).toEqual({
+    checks: [
+      {
+        files: [fixture('mjs-config-file', 'index.js')],
+        name: 'index.js',
+        path: 'index.js'
+      }
+    ],
+    configPath: '.size-limit.mjs',
+    cwd: fixture('mjs-config-file')
+  })
+})
+
+it('should work with .js config file', async () => {
+  expect(await check('js-config-file')).toEqual({
+    checks: [
+      {
+        files: [fixture('js-config-file', 'index.js')],
+        name: 'index.js',
+        path: 'index.js'
+      }
+    ],
+    configPath: '.size-limit.js',
+    cwd: fixture('js-config-file')
+  })
+})
+
+it('should work with .js config file and "type": "module"', async () => {
+  expect(await check('js-config-file-with-type-module')).toEqual({
+    checks: [
+      {
+        files: [fixture('js-config-file-with-type-module', 'index.js')],
+        name: 'index.js',
+        path: 'index.js'
+      }
+    ],
+    configPath: '.size-limit.js',
+    cwd: fixture('js-config-file-with-type-module')
+  })
+})
+
 it('uses peerDependencies as ignore option', async () => {
   expect(await check('peer')).toEqual({
     checks: [