fix: es modules usage in TypeScript when no .babelrc is present (#44)

* fix es modules usage in TypeScript when no .babelrc is present

* only apply ts module transform if target is not already commonjs

Author: yyx990803

lib/compilers/babel-compiler.js

@@ -1,8 +1,8 @@
 const babel = require('babel-core')
 const loadBabelConfig = require('../load-babel-config.js')
 
-module.exports = function compileBabel (scriptContent, inputSourceMap) {
-  const babelConfig = loadBabelConfig()
+module.exports = function compileBabel (scriptContent, inputSourceMap, inlineConfig) {
+  const babelConfig = inlineConfig || loadBabelConfig()
 
   if (!babelConfig) {
     return {

lib/compilers/typescript-compiler.js

@@ -1,6 +1,7 @@
 const tsconfig = require('tsconfig')
 const ensureRequire = require('../ensure-require')
 const compileBabel = require('./babel-compiler')
+const loadBabelConfig = require('../load-babel-config.js')
 const cache = require('../cache')
 const logger = require('../logger')
 
@@ -52,5 +53,16 @@ module.exports = function compileTypescript (scriptContent) {
 
   const res = typescript.transpileModule(scriptContent, tsConfig)
 
-  return compileBabel(res.outputText, JSON.parse(res.sourceMapText))
+  // handle ES modules in TS source code in case user uses non commonjs module
+  // output and there is no .babelrc.
+  let inlineBabelConfig
+  if (tsConfig.compilerOptions.module !== 'commonjs' && !loadBabelConfig()) {
+    inlineBabelConfig = {
+      plugins: [
+        require('babel-plugin-transform-es2015-modules-commonjs')
+      ]
+    }
+  }
+
+  return compileBabel(res.outputText, JSON.parse(res.sourceMapText), inlineBabelConfig)
 }