Hi my question is that we can view the output of symfony
Open the developer tools* in your browser before you make the request on your page. Click on the networks tab then perform the action that makes the request. Click on the request (circled in the chrome example below) and select the Preview tab and you'll see all the output.
* Using Chrome open devtools with the keyboard:
Ctrl+Shift+i or from the menu > More Tools > Developer Tools
Here's an overview of Chrome's devtools. You can breeze through the videos in < 1hr.