In many situations, if you share your URL we can see exactly where the problem lies, but that does obviously require disclosing the URL and not having manually patched jQuery or similar.
For those wanting to play along at home and track down potential culprits, what I do is load up the developer tools (Right click “Inspect” in most cases) and click on the “Console” tab.
When the error occurs it will in most cases have a little drop-down arrow next to it which you can click and see which file originally invoked the command that broke everything (it’ll be near the bottom).
Of course this methods isn’t always available depending on how things were called etc, but you can usually check very quickly for troubles with that approach or just viewing the source of the page.