Which operator is used for string concatenation in JavaScript?

In JavaScript, the operator used for string concatenation is the plus sign (+). When the + operator is used with strings, it combines them into a single string. For example, if you have two string variables, let firstName = "John"; and let lastName = "Doe";, you can concatenate them using let fullName = firstName + " " + lastName;, which would result in the value "John Doe".

This operator is versatile in JavaScript; it can also be used for numerical addition. However, when at least one operand is a string, JavaScript will automatically convert other operands to strings and perform concatenation instead of arithmetic addition. This makes the + operator crucial for managing and manipulating strings in any application that involves user interaction or output display.