read config and pass it to the options

README.md

@@ -316,33 +316,33 @@ let app = new EmberAddon(defaults, {
 
 const { buildEmberPlugins } = require("ember-cli-babel");
 
-module.exports = function (api) {
-  api.cache(true);
-
-  return {
+module.exports = {
     presets: [
       [
-        require.resolve("@babel/preset-env"),
+        "@babel/preset-env",
         {
           targets: require("./config/targets"),
+
+          // do we still need to disable this and manually add modules plugins in the plugins array below?
+          modules: false,
         },
       ],
     ],
     plugins: [
-      // if you want external helpers
+      // if they need/want external helpers
       [
-        require.resolve("@babel/plugin-transform-runtime"),
+        "@babel/plugin-transform-runtime",
         {
-          version: require("@babel/plugin-transform-runtime/package").version,
+          version: "7.12.5",
           regenerator: false,
           useESModules: true,
         },
       ],
-      // this is where all the ember required plugins would reside
-      ...buildEmberPlugins(__dirname, { /*customOptions if you want to pass in */ }),
+
+      // eslint-disable-next-line no-undef
+      ...buildEmberPlugins(__dirname, {}),
     ],
   };
-};
 ```
 
 #### Ember Plugins

index.js

@@ -11,6 +11,7 @@ const {
 
 const VersionChecker = require('ember-cli-version-checker');
 const clone = require('clone');
+const babel = require('@babel/core');
 const path = require('path');
 const fs = require('fs'); 
 const getBabelOptions = require('./lib/get-babel-options');
@@ -92,6 +93,33 @@ module.exports = {
      return options;
   },
 
+  /**
+   * Returns the JSON config of the babel config file.
+   * If its a json config, then return the parsed JSON back
+   * If its a JS config, then load it and return it based on whether its a function or an object.
+   * @param {string} fp babel config file path
+   */
+  _readConfig(fp) {
+    const fileExt = path.extname(fp);
+    switch (fileExt) {
+      case ".json":
+        return JSON.parse(fs.readFileSync(fp));
+      case ".js":
+        try {
+          // eslint-disable-next-line global-require,import/no-dynamic-require
+          const configModule = require(fp);
+          const configJS =
+            configModule && configModule.__esModule
+              ? configModule.default || undefined
+              : configModule;
+          // if the babel config is a function then invoke it, else return the json config.
+          return typeof configJS === "function" ? configJS() : configJS;
+        } catch (error) {
+          error.message = `${fp}: Error while loading config = ${error.message}`;
+          throw error;
+        }
+    }
+  },
   transpileTree(inputTree, _config) {
 
     let config = _config || this._getAddonOptions();
@@ -121,11 +149,7 @@ module.exports = {
           "Missing babel config file in the project root. Please double check if the babel config file exists or turn off the `useBabelConfig` option in your ember-cli-build.js file."
         );
       }
-      options = Object.assign({}, options, {
-        presets: [
-          require.resolve(babelConfigFile),
-        ],
-      });
+      options = Object.assign({}, options, this._readConfig(babelConfigFile));
     } else {
       options = Object.assign({}, options, this.buildBabelOptions(config));
     }

node-tests/addon-test.js

@@ -1605,14 +1605,11 @@ describe('babel config file', function() {
         return prepareAddon(addon);
       });
       let pkg = JSON.parse(fixturifyProject.toJSON('package.json'));
-      fixturifyProject.files['babel.config.js'] = `module.exports = function (api) {
-        api.cache(true);
-        return {
+      fixturifyProject.files['babel.config.js'] = `module.exports = {
           plugins: [
             ${plugins}
           ],
         };
-      };
       `;
       fixturifyProject.writeSync();