javascript - The use of the triple exclamation mark

Question

Looking through the source code of one of our projects, I've found some amount of places where we're using three exclamation marks in conditional statements, like so:

if (!!!someVar) {
    // ...
}

Now, I understand that this isn't some kind of rarely used operator, it's just three negations in a row, like !(!(!someVar))). I don't understand what's the use of it - in my opinion it can safely be replaced with single exclamation mark. Following are my attempts to find a case when !!!a isn't equal to !a (taken straight from the google chrome console):

var a = ''
""
!!!a === !a
true
a = 'string'
"string"
!!!a === !a
true
a = null
null
!!!a === !a
true
a = 12
12
!!!a === !a
true
a = {b: 1}
Object {b: 1}
!!!a.c === !a.c // a.c is undefined here
true
a = []
[]
!!!a === !a
true
a = [1,2]
[1, 2]
!!!a === !a
true

Am I missing some rare (or obvious) case?

Answer 1

There is no difference between !a and !!!a, since !!!a is just !!(!a) and because !a is a boolean, !!(!a) is just its double negation, therefore the same.