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with statement

The with statement

The

with

statement is used to set the scope of the code within a particular object. Its syntax is the

following:

with (

expression

)

statement

;

For example:

var sMessage = “hello world”;

with(sMessage) {

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

}

In this code, the

with

statement is used with a string, so when the

toUpperCase()

method is called, the

interpreter checks to see if this is a local function. If not, it checks the

sMessage

pseudo-object to see if

toUpperCase()

is a method for it, which it is. The alert then outputs

“HELLO WORLD”

because the inter-

preter finds the implementation of

toUpperCase()

on the

“hello world”

string.

The switch statement

The cousin of the

statement, the

switch

statement, allows a developer to provide a series of

cases

for

an expression. The syntax for the switch statement is:

switch (

expression

) {

case

value

statement

break

;

case

value

statement

break

;

case

value

statement

break

;

...

case

value

statement

break

;

default

statement

}

Each case says “if

expression

is equal to

value

, execute

statement

”. The

break

keyword causes code execu-

tion to jump out of the

switch

statement. Without the

break

keyword, code execution falls through the

original case into the following one.

The

default

keyword indicates what is to be done if the expression does not evaluate to one of the

cases (in effect, it is an

else

statement).

The

with

statement is a very slow segment of code, especially while the values of

properties are being set. Most of the time, it’s best to avoid using it if possible.

Chapter 2

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