SourceMap workaround for js files (just that its slightly slower, for speed goto 100% ts)

Author: Shobhit Gupta

config/webpack.config.dev.js

@@ -37,7 +37,7 @@ const env = getClientEnvironment(publicUrl);
 module.exports = {
   // You may want 'eval' instead if you prefer to see the compiled output in DevTools.
   // See the discussion in https://github.com/facebookincubator/create-react-app/issues/343.
-  devtool: 'cheap-module-source-map',
+  devtool: 'source-map',
   // These are the "entry points" to our application.
   // This means they will be the "root" imports that are included in JS bundle.
   // The first two entry points enable "hot" CSS and auto-refreshes for JS.