How do I get an embedded form (iframe) to open a single CRM record for editing using a URL Parameter

I have a form which I want to use to edit a specific record from Zoho CRM Contacts.

Specifically, I want to use the form "onload" to retrieve a single record for editing by

using the current URL parameter value as the record's ID value to be retrieved.

For example, using the form below "id=1234"

So in the deluge script I want to use on form on load event to execute following:

getRec = zoho.crm.getRecordById("Contacts", currentid);

Question is how do I assign:

currentid = 1234

Where 1234 is extracted from URL parameter value "?id=1234"

I looked at getURL but don't think that's quite the solution as it's just the id value required i.e. "1234"

Any suggestions much appreciated!

This post seems to be asking the same question but am not sure about the response on that.

Thanks

Gene