CHAPTER 8
Arrays and Array Processing
JavaScript’s array methods are among my favorite features of the language. So many
programming problems involve the manipulation of collections of data, and fluency
with JavaScript’s array methods will make that easy. Getting comfortable with these
methods is also a great way to attain the next level of JavaScript mastery.
A Review of Arrays
Before we dive in, let’s remind ourselves of the basics of arrays. Arrays (unlike
objects) are inherently ordered, with zero-based numeric indices. Arrays in JavaScript
can be nonhomogeneous, meaning the elements in an array do not need to be the
same type (it follows from this that arrays can have other arrays as elements, or
objects). Literal arrays are constructed with square brackets, and the same square
brackets are used to access elements by index. Every array has a
length
property,
which tells you how many elements are in the array. Assigning to an index that’s
larger than the array will automatically make the array larger, with unused indexes
getting the value
undefined
. You can also use the
Array
constructor to create arrays,
though this is seldom necessary. Make sure all of the following makes sense to you
before you proceed:
// array literals
const
arr1
=
[
1
,
2
,
3
];
// array of numbers
const
arr2
=
[
"one"
,
2
,
"three"
];
// nonhomogeneous array
const
arr3
=
[[
1
,
2
,
3
], [
"one"
,
2
,
"three"
]];
// array containing arrays
const
arr4
=
[
// nonhomogeneous array
{
name
:
"Fred"
,
type
:
"object"
,
luckyNumbers
=
[
5
,
7
,
13
] },
[
{
name
:
"Susan"
,
type
:
"object"
},
{
name
:
"Anthony"
,
type
:
"object"
},
],
1
,
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