Chapter 7 Core Language

Search in book...
Toggle Font Controls
Create new playlist

Name your new playlist

Playlist description (optional)
Sign In

Email address

Password

Forgot Password?

or

Continue with Facebook

Continue with Google
Sign Up

Full Name

Email address

Confirm Email Address

Password

or

Continue with Facebook

Continue with Google

Nav4+, NES3+

Syntax

math.watch( prop, handler )

Description

The watch() method of the Math object will watch for an assignment to a specific property, prop. When an assignment is made, a specified handler will be called to perform a user-defined function. It is inherited from the Object object; however, it cannot be used because math properties are read-only.

Example

Math properties are read-only; therefore, no example is provided.

NaN

JavaScript 1.3+, JScript 1.0+

Nav4.06+, IE3+

Syntax

NaN

Description

The NaN object represents an object that is not equal to any number, including itself. NaN stands for Not a Number.

Example

Listing 7.260 shows how the NaN object is used within a comparison.

Listing 7.260 Example Using the NaN Object

native

JavaScript 1.2+

Nav4+, NES3+

Syntax

Reserved Keyword

Description

The native keyword has not been implemented in server-side JavaScript to date. It has been reserved for future use.

This keyword has not been implemented; therefore, no example is provided.

Number()

JavaScript 1.2+, ECMAScript 1.0+

Nav4+, NES3+, IE5+

Syntax

Number (obj)

Description

The Number() method takes an object, obj, as input and converts it to a number. If the object is a string that is not a well-formed numeric literal, NaN is returned.

Example

Listing 7.263 shows an example of the Number() method. A new Date object is created and converted to a number.

Listing 7.263 Example Number() Method

Number()

JavaScript 1.1+, ECMAScript 1E+, JScript 1.0+

Nav3+, NES2+, IE3+, Opera3+

Syntax

var variable = new Number(value)

Description

The Number() object represents numeric value types. You can create a Number() object by specifying a value in the parameter for the number constructor. Table 7.40 shows the different methods and properties of the Number() object.

Table 7.40 Properties and Methods of the Number() Object

The prototype property of the Number object allows you to add properties or methods to all instances of this class.

Example

Example

Listing 7.278 shows an example for the unwatch() method.

Listing 7.278 Example of unwatch() Method

<html>

<script type=“text/javascript” language=“JavaScript”>

</script>

</html>

Number.valueOf()

JavaScript 1.1+, JScript 2.0+

Nav3+, NES2+, IE4+

Syntax

number.valueOf()

Description

The valueOf() method of the Number object is used to get the primitive value of a Number object as a number data type.

Example

Listing 7.279 shows an example for the valueOf() method. A Number object is created and set to myNum. The document then outputs the result of performing a valueOf function on the number.

Listing 7.279 Example of the Number.valueOf() Method

Number.watch()

JavaScript 1.2+

Nav4+, NES3+

Syntax

JavaScript 1.2+

Nav4+, NES3+

Syntax

Example

Listing 7.295 shows how the parseFloat() is used. In the example, parseFloat() is called with two different strings. The first string, which contains numeric characters, is converted into a number without any problem. The second string, which contains alphabetic characters, is unable to be converted into a number.

Listing 7.295 Example of the parseFloat() Method

<html>
<body>

<script type=“text/javascript” language=“javascript”>

</script>

</body>
</html>

parseInt()

JavaScript 1.0+, ECMAScript 1E+, JScript 1.0+

Nav2+, NES2+, IE3+, Opera3+

Syntax

Listing 7.297 Example of the RegExp Object

<html>
<body>

<script type=“text/javascript” language=“javascript”>

</script>

<form name=“form1”>
Enter your SSN:
<input type=“text” size=“15” name=“ssn”>
<br><br>
<input type=“button” value="Validate SSN" onClick='checkInput()'>
<br>
</form>
</body>
</html>

RegExp,$*

JavaScript 1.2+

Nav4+, NES3+, IE4+

Syntax

RegExp, $*

Description

The RegExp,$* property reflects a multiline string search. This is a Boolean, read-only value that reflects whether strings should be searched across multiple lines. This is the same as using the multiline property.

Example

Listing 7.298 shows how to use RegExp,$* for pattern matching.

Listing 7.298 Example of RegExp,$*

<html>

<script type=“text/javascript” language=“javascript”>

</script>

<body>
<form name=“form1”>
When the text in the text box is changed, and the document is clicked,
an alert box will be displayed showing the value of RegExp.$*.
<br><br>
<textarea name=“mytext” cols=“60” rows=“8” onChange='getinfo()'>
This is a sample textarea containing some dummy text for
testing purposes. The text in this box will be used to
demonstrate how the multiline property is used. If multiple lines are
read, then RegExp.$* will be true.
</textarea>
<br>
</form>

</body>
</html>

RegExp.$&

JavaScript 1.2+, JScript 3.0+

Nav4+, NES3+, IE4+

Syntax

RegExp.$&

Description

The RegExp.$& property represents the last matched characters. This is the same as using the lastMatch property.

JavaScript 1.1+, ECMAScript 1E+

Nav3+, NES2+, IE4+, Opera3+

Syntax

regexp.toString()

Description

The toString() method of the RegExp object is used to get a string representation of the RegExp object.

Example

Listing 7.321 shows how the toString() method is used.

Listing 7.321 Example of the toString() Method

<html>
<body>

<script type=“text/javascript” language=“javascript”>

</script>

</body>
</html>

RegExp.unwatch()

JavaScript 1.2+

Nav4+, NES3+

Syntax

regexp.unwatch(prop)

Description

The unwatch() method of the RegExp object will remove a watch point on a property set by the watch() method.

Example

Listing 7.322 shows an example for the unwatch() method. A property is created using the prototype() method. Then a watch point is placed on the newly created property and a message is displayed when the watch point is hit. When the unwatch() method is called, the watch point is removed.

Listing 7.322 Example of the unwatch() Method

<html>
<body>

<script "type=“text/javascript” language=“javascript”>

</script>
</body>
</html>

RegExp.valueOf()

JavaScript 1.1+

Nav3+, NES2+, IE4+

Syntax

regexp.valueOf()

Description

The valueOf() method of the RegExp object is used to get the primitive value of a RegExp object as a number data type.

Example

Listing 7.323 shows an example for the valueOf() method. A RegExp object is created and set to myExp. The document then outputs the result of performing a valueOf function on the RegExp object.

Listing 7.323 Example of the RegExp.valueOf() Method

RegExp.watch()

JavaScript 1.2+

Nav4+, NES3+

Syntax

regexp.watch(prop, handler)

Description

The watch() method of the RegExp object will watch for an assignment to a specific property. When an assignment is made, a specified handler will be called to perform a user-defined operation.

Example

Listing 7.324 shows an example for the watch() method. A new property is created using the prototype method. Then a watch point is set on the newly created property. When an assignment is made, the alertme function will be called to display a message.

Listing 7.324 Example of the watch() Method

<html>
<body>

<script type=“text/javascript” language=“javascript”>

</script> type="text

</body>
</html>

return

JavaScript 1.0+, JScript 1.0+

Nav2+, NES2+, IE3+, Opera3+

Syntax

return

Description

The return keyword will exit the existing function and return a value.

Example

Example

Example

In Listing 7.330, we will create an instance of the Date object, and then use the String() function to write out a readable string version of the date.

Listing 7.330 Using the String() Function

String (Object)

JavaScript 1.0+, JScript 1.0+, ECMAScript 1E+

Nav2+, NES2+, IE3+, Opera3+

Syntax

var variable = new String(string) JavaScript1.1+
“string”

Description

The String object is one of the core JavaScript objects. Instances are created when a program constructs an instance using the new keyword and passing it the String object. In JavaScript 1.0, instances were also created when programmers quoted characters in their script. Table 7.44 lists the properties and methods used by this object.

Table 7.44 Properties and Methods Used by the String Object

The concat() method of an instance of the String object concatenates the string in string2 to the end of string to return a new string.

Example

Listing 7.338 creates two instances of the String object and uses the concat() method to concatenate them to create a new string. The string is then displayed in an alert box.

Listing 7.338 Using the concat() Method to Concatenate Two Strings

String.constructor

JavaScript 1.1+, JScript 3.0+, ECMAScript 1E+

Nav3+, NES2+, IE4+, Opera3+

Syntax

string.constructor

Description

The constructor property of the String object specifies the function that creates the object.

Listing 7.342 creates an instance of the String object and uses the document.write()method to write two instances of the tag to the page. The results of running this script will be the following:

Hex usage: <font size=“6”>Hello, World!</font>
<br>Color usage: <font size="-2">Hello, World!</font>

Listing 7.342 Using the fontsize() Method of the String Object

String.fromCharCode()

JavaScript 1.2+, JScript 3.0+, ECMAScript 1E+

Nav4+, NES3+, IE4+

Syntax

String.fromCharCode(num1, num2, …, numN)
String.fromCharCode(keyevent.which)

Description

The fromCharCode() method of the String object returns the characters that correspond to the ISO-Latin-1 numbers (num1,num2, …,numN) position passed. You can also pass the method a key event and use the which property to determine which key has been pressed. The possible key events are KeyDown, KeyPress, and KeyUp.

As you can see in the syntax definition, this is a method of the actual String object and not an instance of this object. Because of this, you might want to store the results generated by this method into a variable for future processing.

Example

Listing 7.343 invokes the fromCharCode() method on the numbers 88, 89, and 90. The results of this processing are then written to the user’s page.

Listing 7.343 Using the fromCharCode() Method to Determine the Characters of the ISO-Latin-1 Numbers Passed

String.indexOf()

JavaScript 1.0+, JScript 1.0+, ECMAScript 1E+

Nav2+, NES2+, IE3+, Opera3+

Syntax

string.indexOf(string, num)
string.indexOf(string)

Description

The indexOf() method of an instance of the String object returns the indexed start position of the string passed. Additionally, you can specify an index, defined by num in the syntax definition, to start your search for the string specified. This method is the same as the String.lastIndexOf() method, but it starts at the beginning of the string.

Example

Listing 7.344 creates a simple instance of the String object. This instance is then passed to the indexOf() method on two occasions with the result written to the user’s page. The first occasion looks for a space in the string, which returns 6. The second occasion starts the search at the fourth position, so it returns the location of the letter“l” in the word “world”.

Listing 7.344 Using the indexOf() Method to Find the Location of a Character in a String

String.italics()

Syntax

string.italics()

Description

The italics() method will convert the string it is called on to an instance of the <i>tag.

Example

Example

As the syntax definition states, it is also possible to pass a single index location to the method. In this implementation, the method will not stop at a position and will return all characters until the end of the string.

Example

Listing 7.354 creates an instance of the String object. The slice() method is invoked on this string and asked to return the first seven characters of the string. The results of running this script are written to the user’s page.

Listing 7.354 Using the slice() Method to Return Seven Characters in a String

String.small()

JavaScript 1.0+, JScript 1.0+

Nav2+, NES2+, IE3+, Opera3+

Syntax

string.small()

Description:

The small() method will convert the string it is called on to an instance of the <small>tag.

Example

Listing 7.355 creates an instance of the String object and uses the document.write()method to write the tag to the page. The results of running this script will be the following:

<small>Hello, World!</small>

Listing 7.355 Using the small() Method of the String Object

String.split()

JavaScript 1.1+, JScript 1.0+, ECMAScript 1E+

Nav3+, NES2+, IE3+, Opera3+

Syntax

string.split(separator, num)
string.split(separator)
string.split(regexpression, num)
string.split(regexpression)

Description

The split() method of an instance of the String object splits the string in which it is invoked into separate strings based on the regexpression or separator passed to the method. If a regular expression is passed, it is made up of a pattern and flags that dictate what is to be matched. The separator is a string or character that is matched to perform the separation.

NOTE
If the language attribute of the <script> tag is set to “JavaScript1.2” when using the second syntactical definition and the separator is a space, consecutive spaces are treated differently. In JavaScript 1.1, each space would be split and returned as part of the results. So if there were an instance of three consecutive spaces, two of the spaces would be returned in the array. Specifying JavaScript 1.2 tells the interpreter to treat the three spaces as a single space, so you are able to perform proper splits.

The method returns an array containing each of the segments found in the string.

Listing 7.359 creates an instance of the String object. The substr() method is invoked on this string and asked to return the first six characters of the string. The results of running this script are written to the user’s page.

Listing 7.359 Using the substr() Method to Return Seven Characters in a String

String.substring()

JavaScript 1.0+, JScript 1.0+

Nav2+, NES2+, IE3+, Opera3+

Syntax

string.substring(num1, num2)
string.substring(num)

Description

The substring() method of an instance of the String object returns the characters in the string, starting with the indexed position num1 and ending with the character before num2. The string itself is zero based, so the first character is in position 0.

If you pass num1 as a negative number, it will be treated as 0. Likewise if you pass num2 as a value greater than the String.length property, it will be treated asString.length. And finally, if num1 equals num2, an empty string is returned.

Example

Listing 7.360 creates an instance of the String object. The substring() method is invoked on this string and asked to return the first 10 characters of the string. The results of running this script are written to the user’s page.

Listing 7.360 Using the substring() Method to Return 11 Characters in a String

String.sup()

JavaScript 1.0+, JScript 1.0+

Nav2+, NES2+, IE3+, Opera3+

Syntax

string.sup()

Description

The sup() method will convert the string it is called on to an instance of the <sup> tag.

Example

function String() { [native code] }

If it is invoked on an instance of the String object, it will contain the source of the instance you created.

Example

Listing 7.365 creates an instance of the String object. The toSource() method is then applied to the instance and the results are written to the page. A seconddocument.write() method writes the results of applying the method to the core object.

The result of this application of the method should be something similar to the following:

(new String(<Hello, World!>))

Listing 7.365 Using the toSource() Method of the String Object to Obtain the Source of the Object or an Instance of It

String.toString()

JavaScript 1.1+, JScript1.0+, ECMAScript 1E+

Nav3+, NES2+, IE3+

Syntax

string.toString()
String.toString()

Description

The toString() method of the String object, if invoked on the core String object, will return the object type or the name of the constructor that created the object. This will be something similar to the following:

function String() { [native code] }

Reserved Keyword

Description

The super keyword was reserved for future use but has not currently been implemented.

Example

No example can be provided because super has not been implemented.

switch

JavaScript 1.2+, JScript 3.0+

Nav4+, NES3+, IE4+

Syntax

switch(expression){
case label1:
code;
break;
case label2:
code;
break;
case labelN:
code;
break;
default:
code;
}

Description

The switch statement allows you to process the expression passed by matching it with a label—from label1 to labelN. If there is a match, the code following that label is executed. If the expression passed does not match a label, the default section is executed. Note that you can have as many labels as you deem necessary in your script.

Example

Listing 7.372 has a text field and a button. Users are asked to enter a day of the week into the field. When they press the button, a function is called that contains a switch,

which verifies they entered a correct day. If so, an alert box pops up and tells users what part of the week they entered.

Listing 7.372 Using a switch Statement to Process Data

<html>
<head>
    <title>Using the switch statement</title>
<script type=“text/javascript” language=“JavaScript1.1”>

</script>
</head>
<body>
<form name=“myForm”>
<b>Please enter a day of the week:</b><br>
    <input type=“text” value="" name=“day”>
    <input type=“button” value=“Verify” name=“myButton”
        onClick='verifyDay(this.form)'>
</form>
</body>
</html>

synchronized

JavaScript 1.2+, JScript3.0+

Nav4+, NES3+, IE4+

Syntax

Reserved Keyword

Description

The synchronized keyword has not been implemented in JavaScript to date. It has been reserved for future use.

Example

This keyword has not been implemented; therefore, no example is provided.

this

JavaScript 1.0+, JScript 1.0+

Nav2+, NES2+, IE2+, Opera3+

Syntax

this
this.property

Description

The this keyword is used to refer to the current object and is often used to pass entire objects, such as those contained in Form instances, to functions and methods specified in scripts.

Example

Listing 7.373 contains a text box, a text area, and a button. When the user clicks the button, an onClick event handler passes the form’s information, using the this keyword, to a function defined in the <head> of the document. The function opens a second, smaller window and writes several properties of the form to the page.

Listing 7.373 Using this to Pass All Form Data to a Function

<html>
<head>
    <title>Using this in passing form information</title>
<script type=“text/javascript”>

</script>
</head>
<body>
<form name=“myForm”>
    <textarea name=“myTextArea” rows=2 cols=50>
       Here is some text in my text area.
    </textarea>
    <br>
    <input type=“text” value="Change Me?" name=“myText”>
    <br>
    <input type=“button” value="Display Information" name=“myButton”
        onClick='displayInfo(this.form)'>
</form>
</body>
</html>

Listing 7.374 creates a vehicle object that has three properties: number of doors, color, and the type of vehicle. The this keyword is used to associate these properties with the object when it is referenced in other scripts. Further down in the example, an instance of the vehicle object is created and its properties are written to the page.

Listing 7.374 Using this to Internally Reference Properties of a User-defined Object

<html>
<head>

    <title>Using this in object creation</title>
<script type=“text/javascript”>

</script>
</head>
<body>
<script type=“text/javascript”>

</script>
</body>
</html>

throw

JavaScript 1.4+, JScript 5.0+, ECMAScript 3E+

Nav6+, NES3+, IE5+

Syntax

As soon as an error occurs, the value thrown is passed to the catch clause via exception. If the error cannot be handled, another throw statement is used to pass the error to a higher-level (or next in line) handler if one has been defined.

statement1 is initially where an error can occur. If an if statement is used in the catchclause,exception is only caught if expression is true, at which time statement2 is used to handle the error. If it is not handled,statement3 will be evaluated to handle the exception. As mentioned, if no block can handle the exception, it is passed back to the browser. The finally block, which is optional, is executed before this is done.

Example

Listing 7.376 contains a text box and button. The user is asked to insert a numeric value into the text box and click the button. When this is done, the onClick event handler of the button calls a function to check whether the entered text was numeric. If it is not, the myErrorHandler function is called to handle the error. The myErrorHandler function contains a try…catch…finally statement that allows the programmer to define what happens on an incorrect entry. In this example, an alert box is displayed containing an error code and message; and a second alert box is popped up, within thefinally block, to signal the end of the error processing.

Two levels of error handling are contained in this example to demonstrate nested usage.

Listing 7.376 This Example Uses a try…catch…finally Statement to Handle an Incorrect Entry

<html>
<head>
<script type=“text/javascript” language="JavaScript1.5">

</script>
</head>
<body>
<form name=“myForm”>
    Please enter a number:
    <input type=“text” size=“10” value="" name=“myText”>
    <input type=“button” value=“Process” name=“myButton”
        onClick='processData(this.form)'>
</form>
</body>
</html>

typeof

JavaScript 1.1+, JScript 1.0+

Nav3+, NES2+, IE3+, Opera3+

Syntax

typeof (variable)

Description

The typeof unary operator is used to determine the type of the variable passed to it. The return values of this operator are boolean, number, object, string, or undefined.

Example

Example

Listing 7.380 declares the variable, myVar, in three different locations. It is declared once at a global level, once within a function where it is the returned value, and once in a function where it is written to the page.

Listing 7.380 This Example Shows Using the var Keyword in Three Different Instances

<html>
<head>
    <title>Examples of the var Keyword</title>
<script type=“text/javascript”>

</script>
</head>
<body>
<script type=“text/javascript”>

</script>
</body>
</html>

VBArray

JScript 3.0+

Syntax

var variable = new VBArray(vbarray)

Description

The VBArray object provides access to Visual Basic safeArrays. These arrays are often written on the same HTML page and are written in VBScript. Table 7.45 lists the methods of the VBArray object.

Table 7.45 Methods of the VBArray Object

The void operator is used to evaluate an expression without returning a value. This operator returns undefined and is commonly used in place of the onClick event handler because of various bugs in early Unix Navigator browsers. Note that Opera browsers do not support this operator.

Example

In Listing 7.387, the void operator is used to keep an <a> link on a page from clicking through anywhere while still invoking the function specified.

Listing 7.387 Using the void Operator to Call a Function

<html>
<head>
<title>Examples of the void Operator</title>
<script type=“text/javascript”>

</script>
</head>
<body>
<a HREF="javascript:void(myFunc())">Click here to call the function</A>
</body>
</html>

volatile

JavaScript 1.2+ Nav4+, NES3+

Syntax

Reserved Keyword

Description

The volatile keyword has not been implemented in JavaScript to date. It has been reserved for future use.

Example

This keyword has not been implemented; therefore, no example is provided.

while

JavaScript 1.0+, JScript 1.0+, ECMAScript 1E+

Nav2+, NES2+, IE3+, Opera3+

Syntax

while(condition){
code;
}

Description

The while conditional statement evaluates the condition passed and executes the code within the block until the condition is no longer met. This is often used to evaluate the value of variables, and then perform tasks as well as to iterate through lines in a file when implemented on the server-side.

Example

Listing 7.388 defines a number and then asks the user for a second number. The user is continually asked for the second number until a number lower than the defined number is entered.

Listing 7.388 Using the while Statement to Check the Value Passed In

<html>
<head>
<title>Using while</title>
</head>
<body>
<script type=“text/javascript”>

</script>
</body>
</html>

with

JavaScript 1.0+, JScript 1.0+, ECMAScript 1E+ Nav2+, NES2+, IE3+, Opera3+

Syntax

with(object){
code;
}

Description

The with statement takes an object and refers to all the properties, methods, and events of that object within the code without directly referencing the object itself. This allows you to use these characteristics of an object, such as the Math object, without specifically referencing the object.

Example

Listing 7.389 creates a variable, and then assigns it and the methods called on it, as a Math object. Because the with statement is used, you do not have to reference the methods via the instance of this object.

Listing 7.389 Using the with Statement

..................Content has been hidden....................

You can't read the all page of ebook, please click here login for view all page.

Table of Contents for Chapter 7 Core Language

Create new playlist

Sign In

Sign Up

Math.SQRT2

Syntax

Description

Example

Math.tan()

Syntax

Description

Example

Math.toSource()

Syntax

Description

Example

Math.toString()

Syntax

Description

Example

Math.unwatch()

Syntax

Description

Example

Math.watch()

Syntax

Description

Example

NaN

Syntax

Description

Example

native

Syntax

Description

Example

netscape

Syntax

Description

Example

new

Syntax

Description

Example

null

Syntax

Description

Example

Number()

Syntax

Description

Example

Number()

Syntax

Description

Example

Number.constructor

Syntax

Description

Example

Number.MAX_VALUE

Syntax

Description

Example

Number.MIN_VALUE

Syntax

Description

Example

Number.NaN

Syntax

Description

Example

Number.NEGATIVE_INFINITY

Syntax

Description

Example

Number.POSITIVE_INFINITY

Syntax

Description

Example

Table of Contents for
Chapter 7 Core Language