Changing javascript on the fly on a 3rd party server

Question

JavaScript

Good afternoon
There is a wonderful and beloved site rzd.ru.

Today miraculously discovered that the button to place an order does not work.
I turned on firebug and realized that they had an error in the setCheckedRadioButtonValueToField function (there are a bunch of some incomprehensible checks whether I checked the conditions)

I wanted to quickly fix this code through firebug to “place an order”, but unfortunately I did not find such functionality in firebug.

And actually the question arose - tell me if there are plugins for changing javascript code on the fly?
Those. we have a datafilling.js file - and we want to correct it right there in the window and use the already corrected option.
With what help is it possible to do this?

PS In fact, I need to go through the entire process of buying a ticket just to see my previous order and write out a number for it. I saw the orders button only at the very end of the checkout. It is not clear how many Indians made a website for them.

Answer 1

Greasemonkey? You can execute any script, including overriding a function.

Answer 2

Privoxy ?

Answer 3

I did similar things a little differently
1) Either I simply prepared the html form in the format in which the server requires it
2) Or I executed the script I needed in the console
Based on this, you can try to do this:
- First, add your javascript to the page in the console
- Then redefine the event (button click)

Answer 4

Another option, but works in Opera:

Answer 5

If Opera is installed, then it is possible in it. You open the page, look at the source code, edit everything you need in it, click "Save", return to the checkout page and then you yourself know what to do.
Previously, VKontakte had a JS check for the date of birth. This is how I made myself “Birth year = 1000”