I need a code generator script for Javascript [on hold]

I need help! I'm new to Javascript and what I'm trying to do is too complex for me. I want to have a code that I can put into devtool console that will do a series of commands. I need it to type a code into a text box (It has to be 20 letters long with only uppercase letters and numbers from 0-9) I also need it to execute a button on this website and if the code doesn't work, it loops. So basically it keep typing a random code in and clicking the button until it finds one that works