Step through code

This page describes the JavaScript Debugger as it appears in Firefox 52 and above. To see what it's like in earlier versions of Firefox, see Debugger (before Firefox 52).

If you're using Firefox 52 or later and need to switch back to the old Debugger, you can do so by visiting about:config and setting the "devtools.debugger.new-debugger-frontend" preference to false.

When the debugger is stopped at a breakpoint, you can step through it using four buttons in the toolbar:

In order, the buttons are:

  • Play: run to the next breakpoint
  • Step over: advance to the next line in the same function.
  • Step into: advance to the next line in the function, unless on a function call, in which case enter the function being called
  • Step out: run to the end of the current function

Document Tags and Contributors

 Contributors to this page: wbamberg, grabber24
 Last updated by: wbamberg,