Webmaster''''s Guide to the Wireless Internet part 18 ppt

142 Chapter 4 • Enhancing Client-Side Functionality with WMLScript
Comments are either encapsulated within a pair of “/*” and “*/” or are pre-
ceded with the “//” combination, like this:
/* This is a block of
comments that spans multiple lines
*/
// This is a single line of comment
// This is another line of comment
WMLScript 1.1 also reserves a set of keywords that have special meaning to
the compiler.They are shown in Table 4.2.
Table 4.2 Keywords in WMLScript
access extern path
agent for return
break function typeof
continue header url
div http use
div= if user
Domain isvalid var
else meta while
equiv name
Examining WMLScript Data Types
WMLScript supports five built-in data types:
■
Integer
■
Floating Point
■
String
■
Boolean
■

Invalid
To declare a variable, use the var keyword.There is no need to explicitly
declare the data types;WMLScript will handle them internally.The following
illustrates how WMLScript automatically converts the variable to the appropriate
data type:
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var month=12;
var price=5.95;
var msg="Hello World!";
var printName=true;
var except=Invalid;
The Invalid type is used to differentiate itself from the other data types, for
example:
if (5/0=Invalid) {
// codes here
}
Examining WMLScript Operators
Similar to most programming languages,WMLScript supports the sets of opera-
tors shown in Tables 4.3, 4.4, 4.5, 4.6, and 4.7.
Table 4.3 Assignment Operators
Operator Description
= Assignment
+= Add and then assign; for example, x += y is equivalent to
x = x + y
-= Subtract and then assign; for example, x –= y is equivalent to
x = x – y
*= Multiply and then assign; for example, x *= y is equivalent to
x = x * y

/= Divide and then assign; for example, x /= y is equivalent to
x = x / y
div= Divide (integer division) and then assign; for example,
x div= y is equivalent to x = x div y
%= Remainder (the sign of the result is the same as the sign of the
dividend) and then assign; for example, x %= y is equivalent to
x = x % y
<<= Bitwise left shift and then assign; for example, x <<= y is
equivalent to x = x << y
>>= Bitwise right shift with sign and then assign; for example,
x >>= y is equivalent to x = x >> y
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144 Chapter 4 • Enhancing Client-Side Functionality with WMLScript
>>>= Bitwise right shift zero file and then assign; for example,
x >>>= y is equivalent to x = x >>> y
&= Bitwise AND and then assign; for example, x &= y is equivalent
to x = x & y
^= Bitwise XOR and then assign; for example, x ^= y is equivalent
to x = x ^ y
|= Bitwise OR and then assign; for example, x |= y is equivalent
to x = x | y
Table 4.4 Binary Arithmetic Operators
Operator Description
+ Addition (for number) or concatenation (for strings)
- Subtraction
* Multiplication
/ Division
div Integer division

% Remainder, the sign of the result is the same as the sign of the
dividend
<< Bitwise left shift
>> Bitwise right shift and sign
>>> Bitwise shift right with zero fill
& Bitwise AND
| Bitwise OR
^ Bitwise XOR
Table 4.5 Unary Arithmetic Operators
Operator Description
+ Plus
- Minus
Pre/post decrement
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Table 4.3 Continued
Operator Description
Continued
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Enhancing Client-Side Functionality with WMLScript • Chapter 4 145
++ Pre/post increment
~ Bitwise NOT
Table 4.6 Logical Operators
Operator Description
&& Logical AND
|| Logical OR
! Logical NOT (unary)
Table 4.7 Comparison Operators
Operator Description
< Less than
<= Less than or equal

== Equal
>= Greater than or equal
> Greater than
Inequality
WMLScript also supports the conditional operators. For example, the fol-
lowing if-else statement:
if (x==0) {
x = 1;
}
else {
x=10;
}
can be rewritten as:
x = 0 ? 1 : 10
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Table 4.5 Continued
Operator Description
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146 Chapter 4 • Enhancing Client-Side Functionality with WMLScript
Examining WMLScript Control Structures
WMLScript supports the if construct for making decisions and the while and for
loops for repetitive execution.
Using the If Statement
The if statements allows decisions to be made based on the result of a condition.
For example, the following code snippet will calculate the average if the total is
more than zero; otherwise it will assign the average to be zero:
if (total>0) {
average = sum / total;
} else {
average = 0;

}
Using the While Loop
The while loop executes a block of instruction repeatedly as long as the condition
is true. For example, the following sums up all the integers from 1 to 5:
var num = 5;
var sum = 0;
while (num>=1) {
sum += num—;
}
Using the For Loop
The for loop executes a block of instruction repeatedly for a finite number of
times. For example:
var result = 1;
for (var i=1; i<=num; i++) // loop counter i starts at 1, ends when
result *= i; // i is less than or equal to num. i is
// incremented by 1 in each loop
Using the Break Keyword
The break keyword interrupts the loop within a while or for loop. For example:
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Enhancing Client-Side Functionality with WMLScript • Chapter 4 147
while (num>1) {
sum += num—; // add up num and decrement num by 1
if (sum>20) // if the sum is more than 20,
break; // break out of the loop
}
Using the Continue Keyword
The continue keyword allows execution of either a for or while loop to continue,
thereby skipping the rest of the block. For example:
var num = 20;

for (var i=1; i<=num; i++) {
if (i%2==0) // if no remainder (meaning it is an even number),
continue; // continue the loop
Console.print(i) // else print out the odd number }
Using WMLScript Libraries
The WMLScript specification contains the following libraries:
■
Lang Library Contains functions that relate to the language core.
■
Float Library Contains functions that perform floating point operations.
■
String Library Contains functions that perform string operations.
■
URL Library Contains a set of functions for handling absolute URLs
and relative URLs.
■
WMLBrowser Library Contains functions by which WMLScript can
access the associated WML context.
■
Dialogs Library Contains a set of typical user-interface functions.
Libraries are named collections of functions that belong logically together.To
call these functions, simply specify the library name followed by a dot (.) sepa-
rator and the function name with the appropriate parameters.We will take a look
at some of the examples in the following sections.
The library collection can be extended by emulator vendors for debugging
purposes. For example, the UP.Simulator contains the Console library to help
developers in debugging.
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148 Chapter 4 • Enhancing Client-Side Functionality with WMLScript

Functions in the Class Libraries
Within the libraries there are functions.Table 4.8 shows the functions within the
various libraries described in the previous section.We will be making use of some
of these functions in the examples that follow.
Learning to Interpret WMLScript
Let’s look at our first example on how WML interacts with WMLScript. In this
example, we will look at how a WML deck (see Figure 4.3) calls a WMLScript
program (Figure 4.4) using the <go> element.The WMLScript program in this
example contains one function defined with the extern keyword. It also illustrates
the use of functions located in the libraries.
Figure 4.3
Example1.wml—WML Deck Calling a WMLScript Program
<?xml version="1.0"?>
<!DOCTYPE wml PUBLIC "-//WAPFORUM//DTD WML 1.1//EN"
" /><wml>
<card id="card1" title="Card 1">
<p>
Say hello to WMLScript!
<do type="accept" label="Hello">
<go href="Example1.wmls#Hello" />
</do>
</p>
</card>
</wml>
Figure 4.4 Example1.wmls—WMLScript Program Displaying an Alert
extern function Hello() {
Dialogs.alert("A big Hi from WMLScript!");
}
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149
Table 4.8 Functions of the Various Class Libraries
Lang Float String URL WMLBrowser Dialogs
abort ceil charAt escapeString getCurrentCard alert
abs floor compare getBase getVar confirm
characterSet int elementAt getFragment go prompt
exit maxFloat elements getHost newContext
float minFloat find getParameters prev
isFloat pow format getPath refresh
isInt round insertAt getPort setVar
max sqrt isEmpty getQuery
maxInt length getReferer
min removeAt getScheme
minInt replace isValid
parseFloat replaceAt loadString
parseInt squeeze resolve
random subString unescapeString
seed toString
trim
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150 Chapter 4 • Enhancing Client-Side Functionality with WMLScript
Dissecting the Code
The WML deck (shown in Figure 4.3) contains a <go> element, which points to
a WMLScript file:
<go href="Example1.wmls#Hello" />
To link a WML deck to the WMLScript file, specify the filename of the
WMLScript file in the href attribute of the <go> element.The name following
the # symbol is the function name in the WMLScript.
Within the WMLScript file (see Figure 4.4), we have a function named
Hello() defined with the extern keyword:

extern function Hello() {

}
Only functions in WMLScript with the extern keyword preceding the func-
tion name may be called by a WML deck. In this case, the function named
Hello() accepts no input parameters.
Dialogs.alert("A big Hi from WMLScript!");
This line simply tries to display an alert on the user’s screen. In this case, we
use the alert() function from the Dialogs library. Using the Nokia WAP Toolkit,
you should see the screens shown in Figure 4.5.
NOTE
WMLScript statements end with a semicolon (;). Readers familiar with
JavaScript should feel right at home!
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Figure 4.5 Linking a WML Deck to a WMLScript File
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Enhancing Client-Side Functionality with WMLScript • Chapter 4 151
Performing Mathematical
Operations Using WMLScript
The next example that we will illustrate is performing mathematical operations,
using WMLScript to calculate the factorial of a number.This example uses a
WML deck to prompt the user to enter a number (see Figure 4.6).The number
is then passed to the WMLScript program for calculation (see Figure 4.7).This
example illustrates looping construct in WMLScript as well as setting variable
values in WMLScript and how it is passed back to the WML deck.
Figure 4.6
Example2.wml—WML Deck to Prompt the User to Enter a Number
<?xml version="1.0"?>
<!DOCTYPE wml PUBLIC "-//WAPFORUM//DTD WML 1.1//EN"
" /><wml>

<card id="card1" title="Card 1">
<p>
Factorial machine: <br/>
Enter a number:
<input type="text" name="num" />
<do type="accept" label="Calculate!">
<go href="Example2.wmls#Calculate($(num))" />
</do>
</p>
</card>
<card id="card2" title="Card 2">
<p>
$num ! is $(result)
</p>
</card>
</wml>
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