Uncaught (in promise) SyntaxError: Unexpected token < in JSON at position 0 fetch js code example

Example 1: Uncaught (in promise) SyntaxError: Unexpected token O in JSON at position 0

var stringified = JSON.stringify(data);
var parsedObj = JSON.parse(stringified);
 
console.log(parsedObj);

Example 2: fetch SyntaxError: Unexpected token < in JSON at position 0

JSON.parse(theStringThatIsNotJson);