The expression 'b' + 'a' + + 'a' + 'a' evaluates to 'baNaNa'. Let's break it down: 'b' + 'a' concatenates to 'ba'. Then, + 'a' is the unary plus operator trying to convert 'a' to a number, which results in NaN because 'a' is not a valid numeric string. So, 'ba' + NaN concatenates to 'baNaN'. Finally, 'baNaN' + 'a' concatenates to 'baNaNa'. This example demonstrates both string concatenation and JavaScript's type coercion behavior with the unary plus operator.