tag, which it creates. This attribute can be a number between 1 and 7. If you pass the method the number in the form of a string, the size displayed is relative to the tag.
Example Listing 6.238 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: Hello, World!
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Color usage: Hello, World! Listing 6.238 Using the fontsize() Method of the String Object <script language=”JavaScript”> Size=-2: “ + myString.fontsize(‘-2’)); // Close the stream to the window document.close(); // End hide ––>
String.fromCharCode() JavaScript1.2+, JScript3.0+, ECMAScript1.0+ NES3+, Nav4+, 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 may want to store the results generated by this method into a variable for future processing.
Example Listing 6.239 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 6.239 Using the fromCharCode() Method to Determine the Characters of the ISO-Latin-1 Numbers Passed <script language=”JavaScript1.2”>
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// Invoke the fromCharCode() method and store the results in // a variable. var myString = String.fromCharCode(88,89,90); // Write the results to the page document.write(“These numbers evaluate to: “ + myString); // Close the stream to the page document.close(); // End hide ––>
String.indexOf() JavaScript1.0+, JScript1.0+, ECMAScript1.0+ NES2+, Nav2+, 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 6.240 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 6.240 Using the indexOf() Method to Find the Location of a Character in a String <script language=”JavaScript”> ’); // By specifying an indexed location to start looking you
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// can return the indexed location of the third instance of // the letter ‘l’. document.write(myString.indexOf(“l”, 4)); // Close the stream to the page document.close(); // End hide ––>
String.italics() JavaScript1.0+, JScript1.0+ NES2+, Nav2+, IE3+, Opera3+ Syntax string.italics()
Description The italics() method will convert the string it is called on to an instance of the tag.
Example Listing 6.241 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: Hello, World! Listing 6.241 Using the italics() Method of the String Object <script language=”JavaScript”>
String.lastIndexOf() - 409 -
JavaScript1.0+, JScript1.0+, ECMAScript1.0+ NES2+, Nav2+, IE3+, Opera3+ Syntax string.lastIndexOf(string, num) string.lastIndexOf(string)
Description The lastIndexOf() method of an instance of the String object returns the indexed start position of the string passed, starting from the right and going left. 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.indexOf() method, but it starts at the end of the string.
Example Listing 6.242 creates a simple instance of the String object. This instance is then passed to the lastIndexOf() method on two occasions with the result written to the user’s page. The first occasion looks for the last occurrence of the letter e in the string, which returns 16. The second occasion starts the search at the third position, so it returns the location of the first l in the word “Hello”. Listing 6.242 Using the lastIndexOf() Method to Find the Location of a Character in a String <script language=”JavaScript”> ’); // By specifying an indexed location to start looking, you // can return the indexed location of the second instance of // the letter ‘l’. document.write(myString.lastIndexOf(“l”, 3)); // Close the stream to the page document.close(); // End hide ––>
String.length JavaScript1.0+, JScript1.0+, ECMAScript1.0+ NES2+, Nav2+, IE3+, Opera3+ - 410 -
Syntax string.length
Description The length property of an instance of the String object returns the total length of the string.
Example Listing 6.243 creates three instances of the String object. The length property of each of these instances are accessed and written to the user’s page. Listing 6.243 Accessing the length Property of an Instance of the String Object <script language=”JavaScript”> ”); document.write(myString2 + “: is “ + myString2.length); document.write(“ characters long.
”); document.write(myString3 + “: is “ + myString3.length); document.write(“ characters long.
”); // Close the stream to the page document.close(); // End hide ––>
String.link() JavaScript1.0+, JScript1.0+ NES2+, Nav2+, IE3+, Opera3+ Syntax string.link(URL)
Description The link() method will convert the string it is called on to an instance of the tag, setting the HREF attribute to the URL that is passed.
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Example Listing 6.244 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: The online book! Listing 6.244 Using the link() Method of the String Object <script language=”JavaScript”>
String.match() JavaScript1.2+, JScript3.0+ NES3+, Nav4+, IE4+ Syntax string.match(regexpression)
Description The match() method of an instance of the String object searches the string in which it is invoked for the regular expression passed to the method. The regular expression is made up of a pattern and flags that dictate what is to be matched. The method returns an array containing the matches found in the string. Tip See the reference entry for RegExp for a list of the patterns and flags that can be used to create a regular expression.
Example Listing 6.245 creates an instance of the String object and tries to match instances that contain a space followed by some characters. If any matches were returned into the array, they are written to the user’s page one at a time. Listing 6.245 Using the match() Method to Match Regular Expressions in a String
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<script language=”JavaScript1.2”> ’); // Write the contents of the array to the page. This will put // R, Allen, and Wyke each on a separate line. for(var i = 0; i < answerArray.length; i++){ document.write(answerArray[i] + ‘
’); } } // Close the stream to the window document.close(); // End hide ––>
Operators, S2 String.prototype JavaScript 1.1+, ECMAScript 1.0+, JScript 3.0+ NES2+, Nav3+, IE 4+, Opera3+ Syntax String.prototype.property String.prototype.method
Description The prototype property of the String object allows a programmer to add properties or methods to a core JavaScript object.
Example Listing 6.246 creates two instances of the String object. Then it prototypes a new
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property, type, and a new method, verify(). In the script, the type property is assigned to the string instances and then they are checked using the verify() method. The results of the validation are then written to the user’s page. Listing 6.246 Using the prototype Property to Create New Properties and Methods of the String Object <script language=”JavaScript1.1”> ’); if(myString2.verify()){ document.write(myString2 + “ has a valid type of “ + myString2.type); }else{ document.write(myString2 + “ has an invalid type of “ + myString2.type);
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} // Close the stream to the window //document.close(); // End hide ––>
String.replace() JavaScript1.2+, JScript3.0+ NES3+, Nav4+, IE4+ Syntax string.replace(regexpression, replacestring)
Description The replace() method of an instance of the String object searches the string in which it is invoked for the regular expression passed to the method. The regular expression is made up of a pattern and flags that dictate what is to be matched. If and when a match is found, the method returns a new string with that match replaced with the replacement string passed to the method. Tip See the reference entry for RegExp for a list of the patterns and flags that can be used to create a regular expression.
Example Listing 6.247 creates an instance of the String object. This instance is then searched through to see if any occurrences of the word “Wyke” is found. If so, it is replaced with “White”. Listing 6.247 Using the replace() Method to Replace Regular Expression Matches in a String <script language=”JavaScript1.2”>
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// Close the stream to the window document.close(); // End hide ––>
String.search() JavaScript1.2+, JScript3.0+ NES3+, Nav4+, IE4+ Syntax string.search(regexpression)
Description The search() method of an instance of the String object searches the string in which it is invoked for the regular expression passed to the method. The regular expression is made up of a pattern and flags that dictate what is to be matched. The method returns the indexed start location of the string if it is found and –1 if the string does not contain a regular expression match. Tip See the reference entry for RegExp for a list of the patterns and flags that can be used to create a regular expression.
Example Listing 6.248 creates an instance of the String object, which is searched for the first instance of a space. If a match is found, the indexed start position is returned. The results of running this script are written to the user’s page. Listing 6.248 Using the search() Method to Search Regular Expressions in a String <script language=”JavaScript1.2”>
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// Close the stream to the window document.close(); // End hide ––>
String.slice() JavaScript1.0+, JScript1.0+ NES2+, Nav2+, IE3+, Opera3+ Syntax string.slice(num1, num2) string.slice(num)
Description The slice() method of an instance of the String object returns the characters in the string between the indexed positions num1 and num2 in which the method is invoked. The string itself is zero based, so the first character is in position 0. It is also possible to pass num2 as a negative number. In this scenario, the string counts from the end of the string to end the slice. 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 6.249 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 6.249 Using the slice() Method to Return Seven Characters in a String <script language=”JavaScript”>
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// End hide ––>
String.small() JavaScript1.0+, JScript1.0+ NES2+, Nav2+, 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 6.250 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! Listing 6.250 Using the small() Method of the String Object <script language=”JavaScript1.1”>
String.split() JavaScript1.1+, JScript1.0+, ECMAScript1.0+ NES2+, Nav3+, IE3+, Opera3+ Syntax - 418 -
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 regular expression 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. Tip See the reference entry for RegExp for a list of the patterns and flags that can be used to create a regular expression.
Example Listing 6.251 creates an instance of the String object. This instance is then split, looking for a space as the separator, using each of the syntactical definitions. The results are then written to the user’s page. Listing 6.251 Using the split() Method to Split the String Passed into Separate Strings <script language=”JavaScript1.2”> Currently Evaluating: ‘ + testName + ‘
’); // Check to see if there were any spaces found if(arrayName == null){ document.write(‘No matches were found’); }else{ // Write the contents of the array to the page. This will put // R, Allen, and Wyke each on a separate line. for(var i = 0; i < arrayName.length; i++){ document.write(‘[‘ + i + ‘]: ‘ + arrayName[i] + ‘
’); } } document.write(‘’);
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} // Create an instance of the String object and load it with a name. var myString = new String(“Mr. R. Allen Wyke”); // Define a regular expression and a separator. Both are set to // split on a single whitespace. var myRegExp = /\s/g; var mySeparator = “ “; genResults(myString.split(mySeparator), “Separator Only”); genResults(myString.split(mySeparator, 2), “Separator With Limit of 2”); genResults(myString.split(myRegExp), “Regular Expression Only”); genResults(myString.split(myRegExp, 3), “Regular Expression With Limit of 3”); // Close the stream to the window document.close(); // End hide ––>
String.strike() JavaScript1.0+, JScript1.0+ NES2+, Nav2+, IE3+, Opera3+ Syntax string.strike()
Description The strike() method will convert the string it is called on to an instance of the <strike> tag.
Example Listing 6.252 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: <strike>Hello, World! Listing 6.252 Using the strike() Method of the String Object <script language=”JavaScript”>
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// Write the string to the page after invoking the strike() method on it document.write(myString.strike()); // Close the stream to the window document.close(); // End hide ––>
String.sub() JavaScript1.0+, JScript1.0+ NES2+, Nav2+, IE3+, Opera3+ Syntax string.sub()
Description The sub() method will convert the string it is called on to an instance of the <sub> tag.
Example Listing 6.253 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: <sub>Hello, World! Listing 6.253 Using the sub() Method of the String Object <script language=”JavaScript1.1”>
String.substr() - 421 -
JavaScript1.0+, JScript1.0+ NES2+, Nav2+, IE3+, Opera3+ Syntax string.substr(num1, num2) string.substr(num)
Description The substr() method of an instance of the String object returns the characters in the string, starting with the indexed position num1 and counting to num2 characters. The string itself is zero based, so the first character is in position 0. It is also possible to pass num1 as a negative number. In this scenario, the string starts from the end of the string to begin the substring extraction. 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 6.254 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 6.254 Using the substr() Method to Return Six Characters in a String <script language=”JavaScript1.1”>
String.substring() JavaScript1.0+, JScript1.0+ - 422 -
NES2+, Nav2+, 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 as string.length. And finally, if num1 equals num2, an empty string is returned. 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. Note If the LANGUAGE attribute of the <script> tag is set to “JavaScript1.2” and a Navigator browser is interpreting the script, a runtime out of memory error will be produced if num1 is greater than num2. Without this attribute set, the method returns a substring beginning with num2 and ending with num1 •1.
Example: Listing 6.255 creates an instance of the String object. The substring() method is invoked on this string and asked to return the first ten characters of the string. The results of running this script are written to the user’s page. Listing 6.255 Using the substring() Method to Return Ten Characters in a String <script language=”JavaScript”>
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// End hide ––>
String.sup() JavaScript1.0+, JScript1.0+ NES2+, Nav2+, 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 Listing 6.256 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: <sup>Hello, World! Listing 6.256 Using the sup() Method of the String Object <script language=”JavaScript”>
String.toLowerCase() JavaScript1.0+, JScript1.0+, ECMAScript1.0+ NES2+, Nav2+, IE3+, Opera3+ Syntax string.toLowerCase()
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Description The toLowerCase() method of an instance of a String object converts the characters in that string to all lowercase values. This is often used when a programmer is trying to evaluate a string a user has entered and does not care about case.
Example Listing 6.257 pops up a prompt box and asks the user to enter various case text. After the user clicks OK, the lowercase version of the string is written to the page. Listing 6.257 Using the toLowerCase() Method of the String Object to Convert a String Entered by a User to Lowercase <script language=”JavaScript”>
String.toSource() JavaScript1.3+, JScript3.0+, ECMAScript2.0+ (proposed) Nav4.06+, IE4+ Syntax string.toSource() String.toSource()
Description The toSource() method of the String object is not defined in the first version of the ECMAScript standard, but is proposed for version 2. If this method is invoked on the core String object, it will return something like the following: 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. In Listing 6.258, the result of this application of the method should be something like the following:
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(new String(“Hello, World!”))
Example Listing 6.258 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 second document.write() method writes the results of applying the method to the core object. Listing 6.258 Using the toSource() Method of the String Object to Obtain the Source of the Object or an Instance of It <script language=”JavaScript1.3”> ’); document.write(String.toSource()); // Close the stream to the window document.close(); // End hide ––>
String.toString() JavaScript1.1+, JScript1.0+, ECMAScript1.0+ NES2+, Nav3+, 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 like the following: function String() { [native code] } If it is invoked on an instance of the String object, it will contain the source string of the instance you created. In Listing 6.259, the result of this application of the method should be something like the following:
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Hello, World!
Example Listing 6.259 creates an instance of the String object. The toString() method is then applied to the instance and the results are written to the page. A second document.write() method writes the results of applying the method to the core object. Listing 6.259 Using the toString() Method of the String Object to Obtain the Source of the Object or an Instance of It <script language=”JavaScript1.3”> ’); document.write(String.toString()); // Close the stream to the window document.close(); // End hide ––>
String.toUpperCase() JavaScript1.0+, JScript1.0+, ECMAScript1.0+ NES2+, Nav2+, IE3+, Opera3+ Syntax string.toUpperCase()
Description The toUpperCase() method of an instance of a String object converts the characters in that string to all uppercase values. This is often used when a programmer is trying to evaluate a string a user has entered, and case is not an issue.
Example Listing 6.260 pops up a prompt box and asks the user to enter various case text. After the user clicks OK, the uppercase version of the string is written to the page. Listing 6.260 Using the toUpperCase() Method of the String Object to Convert a String Entered by a User to Uppercase
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<script language=”JavaScript”>
String.valueOf() JavaScript1.1+, JScript3.0+, ECMAScript1.0+ NES2+, Nav3+, IE4+, Opera3+ Syntax string.valueOf()
Description The valueOf() method returns the primitive value of the object. In terms of an instance of a String object, this method returns the string itself.
Example In Listing 6.261, an instance of the String object is created. Since the valueOf() method returns the actual value of the string, “Here is some random text” is written to the user’s page. Listing 6.261 Using the valueOf() Method to Return the Value of the String Instance <script language=”JavaScript1.1”>
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super JavaScript1.3+ NES3+, Nav4.06+ Syntax Reserved Keyword
Description The super keyword was reserved in JavaScript 1.3 for future use but has not currently been implemented.
Example No example can be provided because super has not been implemented.
switch JavaScript1.2+, JScript 3.0+ NES3+, Nav4+, 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 6.262 has a text field and a button. Users are asked to enter a day of the week
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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 6.262 Using a switch Statement to Process Data
Using the switch statement <script language=”JavaScript”>
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// End hide ––>
synchronized JavaScript1.2+, JScript3.0+ NES3+, Nav4+, 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.
Operators, T this JavaScript1.0+, JScript1.0+ NES2+, Nav2+, 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 6.263 contains a text box, a text area, and a button. When the user clicks the
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button, an onClick event handler passes the form’s information, using the this keyword, to a function defined in the of the document. The function opens a second, smaller window and writes several properties of the form to the page. Listing 6.263 Using this to Pass all Form Data to a Function Using this in passing form information <script language=”JavaScript”> The name of the text area is: “); myWin.document.write(form.myTextArea.name); myWin.document.write(“
The value of the button is: “); myWin.document.write(form.myButton.value); // Close the stream to the window myWin.document.close(); } // End hide ––> Listing 6.264 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. The results of running this example are shown in Figure 6.19. Listing 6.264 Using this to Internally Reference Properties of a User-defined Object
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Using this in object creation <script language=”JavaScript”> <script language=”JavaScript”>
Figure 6.19: Results of running Listing 6.264 in a browser.
throw JavaScript1.4+, JScript5.0+ NES3+, Nav5+, IE5+ - 433 -
Syntax throw exception
Description The throw element of the JavaScript language was a reserved keyword in the JavaScript 1.3 and JScript 3.0 languages and in the Netscape Enterprise server 3 environment. Navigator 5 and Internet Explorer 5 were the first browsers to implement the keyword. It is used to generate an error condition handled by a try..catch statement or to pass errors found in these statements to higher level handlers.
Example Listing 6.265 contains a text box and button. The user is asked to insert a numeric value into the text box and press the button. When this is done, the onClick event handler of the button calls a function to check to see if 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 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. Listing 6.265 This Example Uses throw in a try..catch Statement Listing 6.165: Using throw in a try..catch statement <script language=”JScript1.3”>
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// This function reads in the form data and calls the appropriate error. function processData(form){ // Check to see if a number was passed if(isNaN(parseInt(form.myText.value))){ alert(myErrorHandler(“string”)); }else{ alert(“You have correctly entered a number”); } } // End hide ––>
throws JavaScript1.2+ NES3+, Nav4 Syntax Reserved Keyword
Description The throws 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.
transient JavaScript1.2+ NES3+, Nav4+ Syntax Reserved Keyword
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Description The transient 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.
true JavaScript1.2+ NES3+, Nav4+ Syntax Reserved Keyword
Description The true 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.
try...catch JScript5.0+, JavaScript1.4 NES3+, IE5+, Nav5+ Syntax try{ statement1 }catch(exception){ statement2 }
Description The try...catch statement of the JavaScript language contained the try and catch reserve keywords in the JavaScript 1.3 and JScript 3.0 languages and in the Netscape Enterprise server 3 environments. Internet Explorer 5 and Navigator 5 were the first browsers to implement this feature. It can be used to handle all or some of the errors that can occur in a script. If an error is not handled by a try...catch statement, it is passed on so other statements can handle the error. If there are no other statements to handle the error, it is passed to the browser to handle. This usually means a pop-up dialog box to the user or writing the information to the “JavaScript Typein Console” for Navigator 4.06 and higher browsers.
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statement1 is where an error can occur, while statement2 is used to handle the error. As soon as an error occurs, the value thrown is passed to the catch portion of the statement and stored in exception. If the error can not be handled, another throw statement is used to pass the error to a higher level handler if one is defined. Note It is possible to have nested try...catch statements within try...catch statements.
Example Listing 6.266 contains a text box and button. The user is asked to insert a numeric value into the text box and press the button. When this is done, the onClick event handler of the button calls a function to check to see if 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 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. Note that there are two levels of error handling contained in this example to demonstrate nested usage. Listing 6.266 This Example uses a try...catch Statement to Handle an Incorrect Entry Listing 6.166: Using a try..catch statement <script language=”JScript1.3”>
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return(“Error (“ + e + “): Entry was invalid.”); } } // This function reads in the form data and calls the appropriate error. function processData(form){ // Check to see if a number was passed if(isNaN(parseInt(form.myText.value))){ alert(myErrorHandler(“string”)); }else{ alert(“You have correctly entered a number”); } } // End hide ––>
typeof JavaScript1.1+, JScript1.0+ NES2+, Nav3+, 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. Note Because undefined was not fully implemented until JavaScript 1.3 and JScript 3.0, many supporting browsers return null when passing a variable that has not been defined.
Example Listing 6.267 creates boolean, number, object, string, and undefined variable instances, and then uses the typeof operator to write their type to the page.
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Listing 6.267 This Example Uses the typeof Unary Operator to Return the Types for Four Different Variables Listing 6.167: Using typeof to determine the type of variables <script language=”JavaScript1.1”>
variables of different types true; 35; “This is a string”;
// End hide ––> <script language=”JavaScript1.1”> nMyVar = “ + typeof(nMyVar)); document.writeln(“
sMyVar = “ + typeof(sMyVar)); document.writeln(“
uMyVar = “ + typeof(uMyVar)); // End hide ––>
Operators, U -W undefined JavaScript 1.3+, ECMAScript 1.0+, JScript 5.0+ Nav4.06+, IE5+ Syntax undefined
Description The undefined property is a primitive value of the global object. It is returned by variables that have not had values assigned to them. It is also returned by methods if the variable being evaluated is not assigned a value. Browsers not supporting this property return null on the undefined variables.
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Note ECMAScript 1.0 only defines undefined as a primitive value, and does not define it as a property of the global object.
Example Listing 6.268 creates the variable myVariable, and then checks to see if it is undefined in an if clause. Note that Opera 3 and later browsers, even though they do not officially support this property, return null but evaluate the if clause in this example as true. Note At the time of this writing, Internet Explorer 5 was still in beta and incorrectly evaluated the if clause in this example. Listing 6.268 Testing a Variable to See if It is Undefined <script language=”JavaScript1.3”>
unescape() JavaScript 1.0+, JScript 1.0+, ECMAScript 1.0+ NES2+, Nav2+, IE3+, Opera3+ Syntax unescape(string)
Description The unescape() method takes a hexadecimal value and returns the ISO-Latin-1 ASCII equivalent. This method performs the opposite operation of the escape() method and is commonly used to escape user-entered data before form submission.
Example Listing 6.269 declares a local variable, escapedVal, and passes it to the unescape() method. The result, “@”, is then written to the page. Listing 6.269 Using the unescape() Method to Convert a Hexadecimal Value to its ASCII Equivalent
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<script language=”JavaScript”> escapedVal
As you can see in the source, the first item the script determines is if a Windows version of Internet Explorer is trying to render the page. If it is, the isWinIE3 variable is set to true. This is used by the two functions that perform the actual image rollovers. In the body of the page, you will see that an image is placed on the page. Within the tag, you have used the onMouseOut and onMouseOver event handlers to call the appropriate functions. You will also notice that each function takes in a parameter that is the name of the rollover image itself. When the function is called, it evaluates the value of isWinIE3, and then either performs nothing or performs the image swapping. Note Use of the tag is required to call the onMouseOut and onMouseOver event handlers in almost all browsers. Beginning with version 4, however, Internet Explorer provides the ability to include this within the 
