Tool for automatic debugging (debug-tracing step by step) of html page on load?

Question

JavaScript

There is a php script for parsing specific positions in Avito (for personal purposes).
It was convenient - for example, you set up a simulator worth 150 thousand, which is sold for less than 90 thousand for parsing every morning, and if a new ad appears, then the letter arrives in the morning.
However, recently Avito has redone the process, apparently in order to get rid of ... no, not from people like me, but from those who parse numbers there and then spam them.
Sometimes (almost always, but in a real browser it happens so quickly that it seems that the final result is immediately obtained) instead of the result, a "loading in progress" gif is returned, with creepy scripts that after a while already load the real page with the results.
I want to understand how these twisted scripts work.
Those. the browser or some tool needs the following functionality:
1. when opening the page, in the debugger, each action must be performed in steps:
1.1. whether to receive (save) new cookies?
1.2 stopping at the entry point in the loaded javascript procedure, for subsequent step-by-step execution
In the existing chrome console, the developer did not find the possibility that when the page was loaded, nothing was done automatically, but paused, waiting for the user to complete the steps. You can pause in real time only, so you don’t have time to stop in order to understand what is happening.

Answer 1

In chrome, this is called breakpoint
. It works both for generating a house and for js scripts. A
little more details here