Move JSAsset's options gathering code into separate method (#241)

* Move js asset's options code into separate method

* rename getOptions -> getParserOptions

Author: chee

src/assets/JSAsset.js

@@ -34,7 +34,7 @@ class JSAsset extends Asset {
     );
   }
 
-  async parse(code) {
+  async getParserOptions() {
     // Babylon options. We enable a few plugins by default.
     const options = {
       filename: this.name,
@@ -56,6 +56,12 @@ class JSAsset extends Asset {
       options.plugins.push(...file.parserOpts.plugins);
     }
 
+    return options;
+  }
+
+  async parse(code) {
+    const options = await this.getParserOptions();
+
     return babylon.parse(code, options);
   }