feat: add conditional esm exports

Author: jedwards1211

.babelrc.js

@@ -1,18 +1,20 @@
 module.exports = function (api) {
   const plugins = ['@babel/plugin-proposal-class-properties']
+  api.cache.using(() => process.env.OUTPUT_ESM)
   const presets = [
     [
       '@babel/preset-env',
       api.env('es5')
         ? { forceAllTransforms: true }
-        : { targets: { node: '12' } },
+        : {
+            modules: process.env.OUTPUT_ESM ? false : 'auto',
+            targets: { node: '12' },
+          },
     ],
     ['@babel/preset-typescript', { allowDeclareFields: true }],
   ]
 
-  if (api.env(['test', 'coverage', 'es5'])) {
-    plugins.push('@babel/plugin-transform-runtime')
-  }
+  plugins.push('@babel/plugin-transform-runtime')
   if (api.env('coverage')) {
     plugins.push('babel-plugin-istanbul')
   }