The functions that you pass to
find
and
findIndex
, in addition to receiving each ele‐
ment as their first argument, also receive the index of the current element and the
whole array itself as arguments. This allows you to do things, for example, such as
finding square numbers past a certain index:
const
arr
=
[
1
,
17
,
16
,
5
,
4
,
16
,
10
,
3
,
49
];
arr
.
find
((
x
,
i
)
=>
i
>
2
&&
Number
.
isInteger
(
Math
.
sqrt
(
x
)));
// returns 4
find
and
findIndex
also allow you to specify what to use for the
this
variable during
the function invocation. This can be handy if you want to invoke a function as if it
were a method of an object. Consider the following equivalent techniques for search‐
ing for a
Person
object by ID:
class
Person
{
constructor
(
name
) {
this
.
name
=
name
;
this
.
id
=
Person
.
nextId
++
;
}
}
Person
.
nextId
=
0
;
const
jamie
=
new
Person
(
"Jamie"
),
juliet
=
new
Person
(
"Juliet"
),
peter
=
new
Person
(
"Peter"
),
jay
=
new
Person
(
"Jay"
);
const
arr
=
[
jamie
,
juliet
,
peter
,
jay
];
// option 1: direct comparison of ID:
arr
.
find
(
p
=>
p
.
id
===
juliet
.
id
);
// returns juliet object
// option 2: using "this" arg:
arr
.
find
(
p
=>
p
.
id
===
this
.
id
,
juliet
);
// returns juliet object
You’ll probably find limited use for specifying the
this
value in
find
and
findIndex
,
but it’s a technique that you’ll see later, where it is more useful.
Just as we don’t always care about the index of an element within an array, sometimes
we don’t care about the index or the element itself: we just want to know if it’s there or
isn’t. Obviously we can use one of the preceding functions and check to see if it
returns –
1
or
null
, but JavaScript provides two methods just for this purpose:
some
and
every
.
some
returns
true
if it finds an element that meets the criteria (all it needs is one; it’ll
stop looking after it finds the first one), and
false
otherwise. Example:
const
arr
=
[
5
,
7
,
12
,
15
,
17
];
arr
.
some
(
x
=>
x
%
2
===
0
);
// true; 12 is even
arr
.
some
(
x
=>
Number
.
isInteger
(
Math
.
sqrt
(
x
)));
// false; no squares
Array Searching | 137
