In the page source, we see a comment with the base64 encoded stringc3RvcHRoYXRqcw==When we decrypt the string using python, we get>>> import base64>>> b64.decode('c3RvcHRoYXRqcw==')>>> stopthatjsWe use "stopthatjs" as a password, and see the flag appear and quickly disappear.However, the flag still appears in the page source:ABCTF{no(d3)_js_is_s3cur3_dasjkhadbkjfbjfdjbfsdajfasdl}