To remove a role, we simply call
delete()
, which returns
true
if the role was in the
set and
false
otherwise:
roles
.
delete
(
"Admin"
);
// true
roles
;
// Set [ "User" ]
roles
.
delete
(
"Admin"
);
// false
Weak Sets
Weak sets can only contain objects, and the objects they contain may be garbage-
collected. As with
WeakMap
, the values in a
WeakSet
can’t be iterated, making weak sets
very rare; there aren’t many use cases for them. As a matter of fact, the only use for
weak sets is determining whether or not a given object is in a set or not.
For example, Santa Claus might have a
WeakSet
called
naughty
so he can determine
who to deliver the coal to:
const
naughty
=
new
WeakSet
();
const
children
=
[
{
name
:
"Suzy"
},
{
name
:
"Derek"
},
];
naughty
.
add
(
children
[
1
]);
for
(
let
child
of
children
) {
if
(
naughty
.
has
(
child
))
console.log(
`Coal for
${
child
.
name
}
!`
);
else
console.log(
`Presents for
${
child
.
name
}
!`
);
}
Breaking the Object Habit
If you’re an experienced JavaScript programmer who’s new to ES6, chances are
objects are your go-to choice for mapping. And no doubt you’ve learned all of the
tricks to avoiding the pitfalls of objects as maps. But now you have real maps, and you
should use them! Likewise, you’re probably accustomed to using objects with boolean
values as sets, and you don’t have to do that anymore, either. When you find yourself
creating an object, stop and ask yourself, “Am I using this object only to create a
map?” If the answer is “Yes,” consider using a
Map
instead.
Weak Sets | 167
