What is the purpose of the !! (double negation) operator in JavaScript?
The purpose of the !! (double negation) operator in JavaScript is to convert a non-boolean value to its boolean equivalent. The first ! operator converts the value to a boolean and negates it, and the second ! negates it again, resulting in the boolean equivalent of the original value. For example, !!'hello' is true because 'hello' is truthy, while !!0 is false because 0 is falsy. This is equivalent to using the Boolean() function (e.g., Boolean('hello')), but the !! syntax is more concise and is a common idiom in JavaScript code. It's particularly useful when you need a strict boolean value rather than a truthy/falsy value.