Creating Arrays
The easiest way to create an array is with an array literal, which is simply a comma-separated list of array elements within square brackets. For example:
var
empty
=
[];
// An array with no elements
var
primes
=
[
2
,
3
,
5
,
7
,
11
];
// An array with 5 numeric elements
var
misc
=
[
1.1
,
true
,
"a"
,
];
// 3 elements of various types + trailing comma
The values in an array literal need not be constants; they may be arbitrary expressions:
var
base
=
1024
;
var
table
=
[
base
,
base
+
1
,
base
+
2
,
base
+
3
];
Array literals can contain object literals or other array literals:
var
b
=
[[
1
,{
x
:
1
,
y
:
2
}],
[
2
,
{
x
:
3
,
y
:
4
}]];
If an array literal contains multiple commas in a row, with no
value between, the array is sparse (see 7.3). Array elements for which
values are omitted do not exist, but appear to be
undefined
if you query them:
var
count
=
[
1
,,
3
];
// Elements at indexes 0 and 2. count[1] => undefined
var
undefs
=
[,,];
// An array with no elements but a length of 2
Array literal syntax allows an optional trailing comma, so
[,,]
has a lenth of 2, not 3.
Another way to create an array is with the Array()
constructor. You can invoke this
constructor in three distinct ways:
Call it with no arguments:
var
a
=
new
Array
();
This method creates an empty array with no elements and is equivalent to the array literal
[]
.Call it with a single numeric argument, which specifies a length:
var
a
=
new
Array
(
10
);
This technique creates an array with the specified length. This form of the
Array()
constructor can ...
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