I have this piece of code (taken from this question):
var walk = function(dir, done) {
var results = [];
fs.readdir(dir, function(err, list) {
if (err)
return done(err);
var pending = list.length;
if (!pending)
return done(null, results);
list.forEach(function(file) {
file = path.resolve(dir, file);
fs.stat(file, function(err, stat) {
if (stat && stat.isDirectory()) {
walk(file, function(err, res) {
results = results.concat(res);
if (!--pending)
done(null, results);
});
} else {
results.push(file);
if (!--pending)
done(null, results);
}
});
});
});
};
I'm trying to follow it, and I think I understand everything except for near the end where it says !--pending
. In this context, what does that command do?
Edit: I appreciate all the further comments, but the question has been answered many times. Thanks anyway!
!
inverts a value, and gives you the opposite boolean:
!true == false
!false == true
!1 == false
!0 == true
--[value]
subtracts one (1) from a number, and then returns that number to be worked with:
var a = 1, b = 2;
--a == 0
--b == 1
So, !--pending
subtracts one from pending, and then returns the opposite of its truthy/falsy value (whether or not it's 0
).
pending = 2; !--pending == false
pending = 1; !--pending == true
pending = 0; !--pending == false
And yes, follow the ProTip. This may be a common idiom in other programming languages, but for most declarative JavaScript programming this looks quite alien.