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instanceof operator

alert(oStringObject.substring(-3)); //outputs “hello world”

alert(oStringObject.slice(3, -4)); //outputs “lo w”

alert(oStringObject.substring(3,-4)); //outputs “hel”

Here, you see the main difference between

slice()

and

substring()

. When you call each with one

argument,

-3

slice()

returns

“rld”

while

substring()

returns

“hello world”

. This occurs

because

slice(-3)

translates into

slice(7)

for the string

“hello world”

whereas

substring(-3)

translates into

substring(0)

. Likewise, the difference is apparent when using the parameters

and

–4

For the

slice()

method, this translates into

slice(3,7)

, the same as the previous example, which

returns

“lo w”

as the result. However the

substring()

method interprets this as

substring(3,0)

which is essentially

substring(0, 3)

because

substring()

always considers the smaller number as

the start and the larger number as the end. As a result,

substring(3,-4)

returns

“hel”

. The bottom

line here is to be clear about how you are using these two methods.

The last set of methods to be discussed involves case conversion. Four methods perform case conver-

sion:

toLowerCase()

toLocaleLowerCase()

toUpperCase()

, and

toLocaleUpperCase()

. The

uses for these methods are pretty obvious from their names — two convert the string into all lowercase

and two convert the string into all uppercase. The

toLowerCase()

and

toUpperCase()

methods are

the originals, modeled after the same methods in

java.lang.String

; the

toLocaleLowerCase()

and

toLocaleUpperCase()

methods are intended to be implemented based on a particular locale (in the

same way

localeCompare()

is intended to be used). In many locales, the locale-specific methods are

identical to the generic ones; however, a few languages apply special rules to Unicode case conversion

(such as Turkish), and this necessitates using the locale-specific methods for proper conversion.

var oStringObject= new String(“Hello World”);

alert(oStringObject.toLocaleUpperCase()); //outputs “HELLO WORLD”

alert(oStringObject.toUpperCase()); //outputs “HELLO WORLD”

alert(oStringObject.toLocaleLowerCase()); //outputs “hello world”

alert(oStringObject.toLowerCase()); //outputs “hello world”

This code outputs

“HELLO WORLD”

for both

toLocaleUpperCase()

and

toUpperCase()

, just as

“hello world”

is output for both

toLocaleLowerCase()

and

toLowerCase()

. Generally speaking,

if you do not know the language in which the code will be running, it is safer to use the locale-specific

methods.

Remember, all the methods and properties for the

String

class also apply to String primitive values

because they are pseudo-objects.

The instanceof operator

One of the problems with using reference types to store values has been the use of the

typeof

operator,

which returns

“object”

no matter what type of object is being referenced. To provide a solution,

ECMAScript introduced another Java operator:

instanceof

The

instanceof

operator works in a similar way to the

typeof

operator: It identifies the type of object

you are working with. Unlike

typeof

instanceof

requires the developer to explicitly ask if an object is

of a particular type. For example:

var oStringObject = new String(“hello world”);

alert(oStringObject instanceof String); //outputs “true”

Chapter 2

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