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array

As in strings, the first item in an array is in position 0, the second is in position 1, and so on. To access a

particular item, use square brackets enclosing the position of the item to retrieve. For instance, to output

the string

“green”

from the array defined previously, you do this:

alert(aColors[1]); //outputs “green”

The full size of the array can be determined by using the

length

property. Like the same property in

strings, the length property is always one more than the position of the last item, meaning that an array

with three items has items in positions 0 through 2.

var aColors = new Array(“red”, “green”, “blue”);

alert(aColors.length); //outputs “3”

As mentioned previously, the size of an array can grow and shrink as necessary. So, if you wanted to add

another item to the array defined previously, you can just place the value in the next open position:

var aColors = new Array(“red”, “green”, “blue”);

alert(aColors.length); //outputs “3”

aColors[3] = “purple”;

alert(aColors.length); //outputs “4”

In this code, the next open position is 3, so the value

“purple”

is assigned to it. This addition changes

the length of the array from 3 to 4. But what would happen if you placed a value in position 25 of this

array? ECMAScript fills in all positions from 3 to 24 with the value

null

; then it places the appropriate

value in position 25, increasing the size of the array to 26:

var aColors = new Array(“red”, “green”, “blue”);

alert(aColors.length); //outputs “3”

aColors[25] = “purple”;

aColors(arr.length); //outputs “26”

You can also define an

Array

object by using the literal representation, which is indicated by using

square brackets ([ and ]) and separating the values with commas. For instance, the previous example can

be rewritten in the following form:

var aColors = [“red”, “green”, “blue”];

alert(aColors.length); //outputs “3”

aColors[25] = “purple”;

alert(aColors.length); //outputs “26”

Note that, in this case, the

Array

class is never mentioned explicitly. The square brackets imply that the

enclosed values are to be made into an

Array

object. Arrays declared in this way are exactly equal to

arrays declared in the more traditional manner.

Arrays can contain a maximum of 4294967295 items, which should be plenty for

almost all programming needs. If you try to add more than that number, an excep-

tion occurs.

Object Basics

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