This solution only works due to incomplete testing. It checks whether a is truthy. Here are some possible falsy cases in JavaScript:

false,
null,
0,
NaN,
"" (empty string),
undefined

So if you have any value other than these, such as a string like "abc" or simply the boolean true, this function wouldn’t work.

Additionally, even though this is a function expression, which is good practice, you should use the const keyword. Not using it is considered bad practice. And don’t forget the semicolon at the end.

Not entirely true since null or an empty array are falsy. Though when you get a string or a number other than 0, those are truthy. Or what if you have a variable with "true" as its value? Your solution is correct though.

#include <algorithm'> is not necessary here since the function used is part of the string library, not the algorithm library.