feat(load-cfg): add esm module loader

packages/load-cfg/package.json

@@ -21,6 +21,7 @@
     "tslint": "tslint --project ."
   },
   "dependencies": {
+    "esm": "^3.0.41",
     "deepmerge": "^2.1.1",
     "find-up": "^2.1.0"
   },

packages/load-cfg/src/index.ts

@@ -2,14 +2,13 @@ import * as fs from 'fs'
 import * as path from 'path'
 import findup from 'find-up'
 import merge from 'deepmerge'
+import esm from 'esm'
 
 export const finds = (name: string): string[] => [
   `${name}.json`,
   `.${name}rc`,
   `${name}rc.js`,
   `${name}rc.json`,
-  `${name}rc.yml`,
-  `${name}rc.yaml`,
   `${name}.config.js`,
   `${name}.config.json`,
 ]
@@ -20,6 +19,12 @@ export const loadFile = (
   noCache?: boolean
 ) => {
   let file
+  const require = esm(module, {
+    cache: !noCache,
+    cjs: {
+      cache: !noCache,
+    },
+  })
 
   if (noCache && filepath) {
     delete require.cache[path.resolve(filepath)]
@@ -28,9 +33,12 @@ export const loadFile = (
   try {
     const isJS = path.extname(filepath) === '.js'
 
-    file = isJS
-      ? require(filepath)
-      : JSON.parse(fs.readFileSync(filepath, 'utf-8'))
+    if (isJS) {
+      const required = require(filepath)
+      file = required.default || required
+    } else {
+      file = JSON.parse(fs.readFileSync(filepath, 'utf-8'))
+    }
   } catch (err) {
     file = defaultFile
   }

packages/load-cfg/src/types.d.ts

@@ -1 +1,2 @@
 declare module 'deepmerge'
+declare module 'esm'

yarn.lock

@@ -3359,6 +3359,10 @@ eslint@^4.1.1:
     table "4.0.2"
     text-table "~0.2.0"
 
+esm@^3.0.41:
+  version "3.0.41"
+  resolved "https://registry.npmjs.org/esm/-/esm-3.0.41.tgz#f7e8678510e5da89afc5709f9fc1c87f289919e9"
+
 espree@^3.5.4:
   version "3.5.4"
   resolved "https://registry.npmjs.org/espree/-/espree-3.5.4.tgz#b0f447187c8a8bed944b815a660bddf5deb5d1a7"