Breakpoint on any string assignment if string contains a certain substring

Can I put a data breakpoint which triggers if any variable is assigned to a string containing a certain substring?

For example, I want to reverse-engineer how a URL containing &ctoken= is constructed. It's done with complicated JavaScript where the goal is to obfuscate it.

If I could tell the JS VM to monitor all string variables and break when a certain substring appears on any variable, this would help me a lot.

Is this possible?