Which of the following string operations tends to be the least efficient for large-scale string manipulations?
Using the string addition operator (+) in a loop tends to be the least efficient operation for large-scale string manipulations. Strings in JavaScript are immutable, meaning each string concatenation with the + operator creates a new string in memory. When done repeatedly in a loop, this leads to a quadratic time complexity O(n²) behavior as each iteration creates a new, progressively longer string. For large-scale string concatenation, more efficient alternatives include: 1) Building an array of strings and joining them with Array.prototype.join() at the end, 2) Using a specialized string builder-like object, or 3) Using template literals for simpler concatenations. Modern JavaScript engines have optimized template literals and simple concatenation, but the loop pattern still remains problematic for large strings.