Appendix C_ Answers to Tutorial Exercises

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1. The music jukebox (a) and temperature calculator (d) are good client-side JavaScript applications. Even though the jukebox relies on server storage of the music ﬁles, you can create a more engaging and responsive user interface of buttons, swappable images, and information from a plug-in, such as LiveAudio. The temperature calculator is a natural, because all processing is done instantaneously on the client, rather than having to access the server for each conversion.

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Nội dung Text: Appendix C_ Answers to Tutorial Exercises

Answers to Tutorial C A P P E N D I X Exercises 3 3 3 3 T his appendix provides answers to the tutorial exercises that appear in Part II of this book (Chapters 4 through 12). Chapter 4 Answers 1. The music jukebox (a) and temperature calculator (d) are good client-side JavaScript applications. Even though the jukebox relies on server storage of the music ﬁles, you can create a more engaging and responsive user interface of buttons, swappable images, and information from a plug-in, such as LiveAudio. The temperature calculator is a natural, because all processing is done instantaneously on the client, rather than having to access the server for each conversion. The Web site visit counter ( b) that accumulates the number of different visitors to a Web site is a server- side CGI application, because the count must be updated and maintained on the server. At best, a client- side counter could keep track of the number of visits the user has made to a site and report to the user how many times he or she has been to the site. The storage would require scripting the cookie (Chapter 16). A chat room application (c) done properly requires server facilities to open up communication channels among all users connected simultaneously. Client-side scripting by itself cannot create a live chat environment. 2. The ﬁrst task is to determine a valid identiﬁer for the General Motors location in the hierarchy. Then “connect the dots”:
954 Part V 3 Appendixes a. General_Motors.Chevrolet.Malibu b. General_Motors.Pontiac.Firebird c. General_Motors.Pontiac.Bonneville 3. a. Valid, because it is one contiguous word. InterCap spelling is ﬁne. b. Valid, because an underscore character is acceptable between words. c. Not valid, because an identiﬁer cannot begin with a numeral. d. Not valid, because no spaces are allowed. e. Not valid, because apostrophes and most other punctuation are not allowed. 4. The names I assign here are arbitrary, but the paths are not. document.myPicture document.entryForm document.entryForm.nameField document.entryForm.addressField document.entryForm.phoneField document.entryForm.noArchiveBox window frame self top parent history document location toolbar, etc. form image text text checkbox reset submit text 5. Chapter 5 Answers 1.
Appendix C 3 Answers to Tutorial Exercises 955 2. 3. 4. My answer is written so that both event handlers call separate functions. You can also have each event handler invoke the alert() method inline. An onLoad= script Here is some body text. 5. a. The page displays two text ﬁelds. b. The user enters text into the ﬁrst ﬁeld and either clicks or tabs out of the ﬁeld to trigger the onChange= event handler. c. The function displays an all-uppercase version of one ﬁeld into the other.
956 Part V 3 Appendixes Chapter 6 Answers 1. a. Valid. b. Not valid. The variable needs to be a single word, such as howMany or how_many. c. Valid. d. Not valid. The variable name cannot begin with a numeral. If the variable needs a number to help distinguish it from other similar variables, then put the numeral at the end: address1. 2. a. 4 b. 40 c. “4020” d. “Robert” 3. The functions are parseInt() and parseFloat(). Strings to be converted are passed as parameters to the functions: parseInt(document.forms[0].entry.value). 4. Both text ﬁeld values are strings that must be converted to numbers before they can be arithmetically added together. You can use the parseFloat() functions either on the variable assignment expressions (for example, var value1 = parseFloat(document.adder.inputA.value)) or in the addition expression (document.adder.output.value = parseFloat(value1) + parseFloat(value2)). 5. Concatenate means to join together two strings to become one string. Chapter 7 Answers 1. Because the references in the function point to a text ﬁeld named entry inside a form named entryForm, be sure to assign those names to the NAME attributes in the respective HTML tags. var USStates = new Array(51) USStates[0] = “Alabama” USStates[1] = “Alaska” USStates[2] = “Arizona” USStates[3] = “Arkansas” USStates[4] = “California” USStates[5] = “Colorado” USStates[6] = “Connecticut” USStates[7] = “Delaware” USStates[8] = “District of Columbia”
Appendix C 3 Answers to Tutorial Exercises 957 USStates[9] = “Florida” USStates[10] = “Georgia” USStates[11] = “Hawaii” USStates[12] = “Idaho” USStates[13] = “Illinois” USStates[14] = “Indiana” USStates[15] = “Iowa” USStates[16] = “Kansas” USStates[17] = “Kentucky” USStates[18] = “Louisiana” USStates[19] = “Maine” USStates[20] = “Maryland” USStates[21] = “Massachusetts” USStates[22] = “Michigan” USStates[23] = “Minnesota” USStates[24] = “Mississippi” USStates[25] = “Missouri” USStates[26] = “Montana” USStates[27] = “Nebraska” USStates[28] = “Nevada” USStates[29] = “New Hampshire” USStates[30] = “New Jersey” USStates[31] = “New Mexico” USStates[32] = “New York” USStates[33] = “North Carolina” USStates[34] = “North Dakota” USStates[35] = “Ohio” USStates[36] = “Oklahoma” USStates[37] = “Oregon” USStates[38] = “Pennsylvania” USStates[39] = “Rhode Island” USStates[40] = “South Carolina” USStates[41] = “South Dakota” USStates[42] = “Tennessee” USStates[43] = “Texas” USStates[44] = “Utah” USStates[45] = “Vermont” USStates[46] = “Virginia” USStates[47] = “Washington” USStates[48] = “West Virginia” USStates[49] = “Wisconsin” USStates[50] = “Wyoming” var stateEntered = new Array(51) stateEntered[0] = 1819 stateEntered[1] = 1959 stateEntered[2] = 1912 stateEntered[3] = 1836 stateEntered[4] = 1850 stateEntered[5] = 1876 stateEntered[6] = 1788 stateEntered[7] = 1787 stateEntered[8] = 0000
958 Part V 3 Appendixes stateEntered[9] = 1845 stateEntered[10] = 1788 stateEntered[11] = 1959 stateEntered[12] = 1890 stateEntered[13] = 1818 stateEntered[14] = 1816 stateEntered[15] = 1846 stateEntered[16] = 1861 stateEntered[17] = 1792 stateEntered[18] = 1812 stateEntered[19] = 1820 stateEntered[20] = 1788 stateEntered[21] = 1788 stateEntered[22] = 1837 stateEntered[23] = 1858 stateEntered[24] = 1817 stateEntered[25] = 1821 stateEntered[26] = 1889 stateEntered[27] = 1867 stateEntered[28] = 1864 stateEntered[29] = 1788 stateEntered[30] = 1787 stateEntered[31] = 1912 stateEntered[32] = 1788 stateEntered[33] = 1789 stateEntered[34] = 1889 stateEntered[35] = 1803 stateEntered[36] = 1907 stateEntered[37] = 1859 stateEntered[38] = 1787 stateEntered[39] = 1790 stateEntered[40] = 1788 stateEntered[41] = 1889 stateEntered[42] = 1796 stateEntered[43] = 1845 stateEntered[44] = 1896 stateEntered[45] = 1791 stateEntered[46] = 1788 stateEntered[47] = 1889 stateEntered[48] = 1863 stateEntered[49] = 1848 stateEntered[50] = 1890 function getStateDate() { var selectedState = document.entryForm.entry.value for ( var i = 0; i < USStates.length; i++) { if (USStates[i] == selectedState) { break } } alert(“That state entered the Union in “ + stateEntered[i] + “.”) }
Appendix C 3 Answers to Tutorial Exercises 959 Enter the name of a state: 2. Several problems plague this function deﬁnition. Parentheses are missing from the ﬁrst if construction’s condition statement. Curly braces are missing from the second nested if...else construction. A mismatch of curly braces also exists for the entire function. The following is the correct form (changes and additions in boldface): function format(ohmage) { var result if (ohmage >= 10e6) { ) ohmage = ohmage / 10e5 result = ohmage + “ Mohms” } else { if (ohmage >= 10e3) { ohmage = ohmage / 10e2 result = ohmage + “ Kohms” } else { result = ohmage + “ ohms” } } alert(result) } 3. Here is one possibility: for (var i = 1; i < tomatoes.length; i++) { if (tomatoes[i].looks == “mighty tasty”) { break } } var myTomato = tomatoes[i] 4. The new version deﬁnes a different local variable name for the dog. var aBoy = “Charlie Brown” // global var hisDog = “Snoopy” // global function sampleFunction() { // using improper design to demonstrate a point var WallacesDog = “Gromit” // local version of hisDog var output = WallacesDog + “ does not belong to “ + aBoy + “.” document.write(output)
960 Part V 3 Appendixes } sampleFunction() // runs as document loads document.write(hisDog + “ belongs to “ + aBoy + “.”) 5. The application uses three parallel arrays and is structured very much like the solution to question 1. Learn to reuse code whenever you can. var planets = new Array(4) planets[0] = “Mercury” planets[1] = “Venus” planets[2] = “Earth” planets[3] = “Mars” var distance = new Array(4) distance[0] = “36 million miles” distance[1] = “67 million miles” distance[2] = “93 million miles” distance[3] = “141 million miles” var diameter = new Array(4) diameter[0] = “3100 miles” diameter[1] = “7700 miles” diameter[2] = “7920 miles” diameter[3] = “4200 miles” function getPlanetData() { var selectedPlanet = document.entryForm.entry.value for ( var i = 0; i < planets.length; i++) { if (planets[i] == selectedPlanet) { break } } var msg = planets[i] + “ is “ + distance[i] + “ from the Sun and “ msg += diameter[i] + “ in diameter.” document.entryForm.output.value = msg } Enter the name of a planet:
Appendix C 3 Answers to Tutorial Exercises 961 Chapter 8 Answers 1. a. Close, but no cigar. Array references are always plural: window.document.forms[0]. b. Not valid: self refers to a window and entryForm must refer to a form. Where’s the document? It should be self.document.entryForm.entryField.value. c. Valid. d. Not valid. The document reference is missing from this one. e. Valid, assuming that newWindow is a variable holding a reference to a subwindow. 2. window.status = “Welcome to my Web page.” 3. document.write(“Welcome to my Web page.”) 4. A script in the Body portion invokes a function that returns the text entered in a prompt() dialog box. function askName() { var name = prompt(“What is your name, please?”,””) return name } document.write(“Welcome to my web page, “ + askName() + “.”) 5. The URL can be derived from the location object. function showLocation() { alert(“This page is at: “ + location.href) }
962 Part V 3 Appendixes Blah, blah, blah. Chapter 9 Answers 1. For Listing 9-1, pass the text object because that’s the only object involved in the entire transaction. Text Object value Property function upperMe(ﬁeld) { ﬁ ﬁeld.value = ﬁeld.value.toUpperCase() } t For Listing 9-2, the button invokes a function that communicates with a different element in the form. Pass the form object. Checkbox Inspector function inspectBox(form) { f if (form.checkThis.checked) { f alert(“The box is checked.”) } else { alert(“The box is not checked at the moment.”) } } Check here t For Listing 9-3, again the button invokes a function that looks at other elements in the form. Pass the form object.
Appendix C 3 Answers to Tutorial Exercises 963 Extracting Highlighted Radio Button function fullName(form) { f for (var i = 0; i < form.stooges.length; i++) { if (form.stooges[i].checked) { break } } alert(“You chose “ + form.stooges[i].value + “.”) } Select your favorite Stooge: Moe Larry Curly t For Listing 9-4, all action is triggered by and conﬁned to the select object. Pass only that object to the function. Select Navigation function goThere(list) { l location = list.options[list.selectedIndex].value } Choose a place to go: t Home Page Shop Our Store Shipping Policies Search the Web
964 Part V 3 Appendixes 2. This requires a bit of surgery. The Submit button is replaced with a standard button whose VALUE attribute is set to “Submit.” The button’s onClick= event handler calls the checkForm() function, which performs the validation. If an empty ﬁeld exists, the function must return to bail out of the loop. Because the event handler is not expecting any returned value, you can simply issue the return statement to stop the function altogether. If all the tests pass, then the form is submitted with the submit() method. Functions that have a return statement inside an if construction must also have a return statement outside the construction so it always returns a value (including the null value used here). The other change is that the onSubmit= event handler has been removed from the tag, because it is no longer needed (the submit() method does not trigger an onSubmit= event handler). Validator function checkForm(form) { for (var i = 0; i < form.elements.length; i++) { if (form.elements[i].value == “”) { alert(“Fill out ALL ﬁelds.”) return } } form.submit() return } Please enter all requested information: First Name: Last Name: Rank: Serial Number: 3. The this keyword refers to the text ﬁeld object, so this.value refers to the value property of that object. function showText(txt) { alert(txt) } 4. document.accessories.acc1.value = “Leather Carrying Case” document.forms[1].acc.value = “Leather Carrying Case”
Appendix C 3 Answers to Tutorial Exercises 965 5. The select object invokes a function that does the job. Color Changer function setColor(list) { var newColor = list.options[list.selectedIndex].value document.bgColor = newColor } Select a background color: Stop Caution Go Chapter 10 Answers 1. Use string.indexOf() to see if the ﬁeld contains the “@” symbol. E-mail Validator function checkAddress(form) { if (form.email.value.indexOf(“@”) == -1) { alert(“Check the e-mail address for accuracy.”) return false } return true } Enter your e-mail address:
966 Part V 3 Appendixes 2. Remember that the substring goes up to, but does not include, the index of the second parameter. Spaces count as characters. myString.substring(0,3) // result = “Net” myString.substring(13,18) // result = “gator” myString.substring(4,12) // result = “cape Nav” 3. The missing for loop is in boldface. You could also use the increment operator on the count variable (++count) to add 1 to it for each letter “e.” function countE(form) { var count = 0 var inputString = form.mainstring.value.toUpperCase() for (var i = 0; i < inputString.length; i++) { if (inputStr.charAt(i) == “e”) { count += 1 } } alert(“The string has “ + count + “ instances of the letter e.”) } 4. The formula for the random throw of one die is in the chapter. E-mail Validator function roll(form) { form.die1.value = Math.round(Math.random() * 5) + 1 form.die2.value = Math.round(Math.random() * 5) + 1 } 5. If you used the Math.round() method in your calculations, that is ﬁne for your current exposure to the Math object. Another method, Math.ceil(), may be more valuable because it rounds up any fractional value. Waiting for Santa function daysToXMAS() { var oneDay = 1000 * 60 * 60 * 24
Appendix C 3 Answers to Tutorial Exercises 967 var today = new Date() var XMAS = new Date(“December 25, 1998”) var diff = XMAS.getTime() - today.getTime() return Math.ceil(diff/oneDay) } document.write(daysToXMAS() + “ days until next Christmas.”) Chapter 11 Answers 1. onLoad=”parent.currCourse = ‘history101’” 2. 3. All three frames are siblings, so references include the parent. parent.mechanics.location.href = “french201M.html” parent.description.location.href = “french201D.html” 4. A script in one of the documents is attempting to reference the selector object in one of the frames but the document has not fully loaded, causing the object to not yet be in the browser’s object model. Rearrange the script so that it ﬁres in response to the onLoad= event handler of the framesetting document.
968 Part V 3 Appendixes 5. From the subwindow, the opener property refers back to the frame containing the window.open() method. To extend the reference to the frame’s parent, the reference includes both pieces: opener.parent.ObjVarFuncName. Chapter 12 Answers 1. A document image object is created by the tag as the document loads. A memory image object is created with the new Image() constructor. Both objects have the same properties, and assigning a URL to the src property of a memory object loads the image into the browser’s image cache. 2. var janeImg = new Image(100,120) janeImg.src = “jane.jpg” 3. document.images[“people”].src = janeImg.src 4. Surround tags with link tags, and use the link’s onClick=, onMouseOver=, and onMouseOut= event handlers. Set the image’s BORDER attribute to zero if you don’t want the link highlight to appear around the image. 3 3 3