Putting this in my web console:

  let susJsonString=JSON.stringify(JSON.stringify(JSON.stringify({foo:1})))
  console.log("initial:", susJsonString);
  try { 
    while(typeof susJsonString==='string') {
        susJsonString = JSON.parse(susJsonString);
        console.log("iteration:", typeof susJsonString, susJsonString);
    }
  } catch {
    susJsonString = {};
  }

I see:

  initial: "\"{\\\"foo\\\":1}\""
  iteration: string "{\"foo\":1}"
  iteration: string {"foo":1}
  iteration: object {foo: 1}

A comment explaining the sort of "sus" input it was designed to cope with may have been helpful.