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1005Chapter 37 .The Array Object array.toLocaleString() Returns: String. NN2 NN3 NN4 NN6 IE3/J1 IE3/J2 IE4 IE5 IE5.5 Compatibility . array.toString() Returns: String. NN2 NN3 NN4 NN6 IE3/J1 IE3/J2 IE4 IE5 IE5.5 Compatibility . . . The array.toLocaleString() and the older, more compatible array.toString() are methods to retrieve the contents of an array in string form. Browsers use the toString() method on their own whenever you attempt to display an array in text boxes, in which case the array items are comma-delimited. The precise string conversion of the toLocaleString() is left up to the specific browser implementation. That IE5.5 and NN6 differ in some details is not surprising, even in the U.S. English versions of operating systems and browsers. For example, if the array contains integer values, IE5.5 s toLocaleString()method returns the numbers comma-and-space-delimited, formatted with two digits to the right of the decimal (as if dollars and cents). NN6, on the other hand, returns just the integers, but these are also comma-and-space-delimited. If you need to convert an array to a string for purposes of passing array data to other venues (for example, as data in a hidden text box submitted to a server or as search string data conveyed to another page), use the array.join() method instead. Array.join()gives you more reliable and flexible control over the item delimiters, and you are assured of the same results regardless of locale. Related Items: array.join() method. … array.toString()
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1004 Part IV . JavaScript Core Language Reference Example (with Listing 37-9) on the CD-ROM On the CD-ROM Note Related Items: array.reverse() method. As I show you in Chapter 38, many regular expression object methods generate arrays as their result (for example, an array of matching values in a string). These special arrays have a custom set of named properties that assist your script in analyzing the findings of the method. Beyond that, these regular expression result arrays behave like all others. array.splice(startIndex , deleteCount[, item1[, item2[,…itemN]]]) Returns: Array. NN2 NN3 NN4 NN6 IE3/J1 IE3/J2 IE4 IE5 IE5.5 Compatibility . . If you need to remove items from the middle of an array, the array.splice() method (not implemented in IE5/Mac) simplifies a task that would otherwise require assembling a new array from selected items of the original array. The first of two required parameters is a zero-based index integer that points to the first item to be removed from the current array. The second parameter is another integer that indicates how many sequential items are to be removed from the array. Removing array items affects the length of the array, and those items that are removed are returned by the splice()method as their own array. You can also use the splice() method to replace array items. Optional parame ters beginning with the third let you provide data elements that are to be inserted into the array in place of the items being removed. Each added item can be any JavaScript data type, and the number of new items does not have to be equal to the number of items removed. In fact, by specifying a second parameter of zero, you can use splice()to insert one or more items into any position of the array. On the CD-ROM Example on the CD-ROM Related Items: array.slice() method. array.splice()
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1003Chapter 37 .The Array Object hand, if ais smaller than b, then the returned negative value tells sort() to put a in a lower index value spot than b. Evaluations within the comparison function can go to great lengths, as long as some data connected with array values can be compared. For example, instead of numerical comparisons, as just shown, you can perform string comparisons. The following function sorts alphabetically by the last character of each array string entry: function compare(a,b) { // last character of array strings var aComp = a.charAt(a.length - 1) var bComp = b.charAt(b.length - 1) if (aComp < bComp) {return -1} if (aComp > bComp) {return 1} return 0 } First, this function extracts the final character from each of the two values passed to it. Then, because strings cannot be added or subtracted like numbers, you compare the ASCII values of the two characters, returning the corresponding values to the sort()method to let it know how to treat the two values being checked at that instant. When an array s entries happen to be objects, you can even sort by properties of those objects. If you bear in mind that the a and bparameters of the sort function are references to two array entries, then by extension you can refer to properties of those objects. For example, if an array contains objects whose properties define information about employees, one of the properties of those objects can be the employee s age as a string. You can then sort the array based on the numeric equivalent of ageproperty of the objects by way of the following comparison function: function compare(a,b) { return parseInt(a.age) - parseInt(b.age) } Array sorting, unlike sorting routines you may find in other scripting languages, is not a stable sort. Not being stable means that succeeding sort routines on the same array are not cumulative. Also, remember that sorting changes the sort order of the original array. If you don t want the original array harmed, make a copy of it before sorting or reload the document to restore an array to its original order. Should an array element be null, the method sorts such elements at the end of the sorted array starting with Navigator 4 (instead of leaving them in their original places as in Navigator 3). Note Unfortunately, this powerful method does not work in the Macintosh version of Navigator 3. Starting with Navigator 4, all platforms have the feature. JavaScript array sorting is extremely powerful stuff. Array sorting is one reason why it s not uncommon to take the time during the loading of a page containing an IE XML data island to make a JavaScript copy of the data as an array of objects (see Chapter 57). Converting the XML to JavaScript arrays makes the job of sorting the data much easier and faster than cobbling together your own sorting routines on the XML elements. array.sort()
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1002 Part IV . JavaScript Core Language Reference Look first at the kind of sorting you can do with the array.sort()method by itself (for example, without calling a comparison function). When no parameter is specified, JavaScript takes a snapshot of the contents of the array and converts items to strings. From there, it performs a string sort of the values. ASCII values of characters govern the sort, which means that numbers are sorted by their string values, not their numeric values. This fact has strong implications if your array con sists of numeric data: The value 201 sorts before 88, because the sorting mecha nism compares the first characters of the strings ( 2 versus 8 ) to determine the sort order. For simple alphabetical sorting of string values in arrays, the plain array.sort() method does the trick. Fortunately, additional intelligence is available that you can add to array sorting. The key tactic is to define a function that helps the sort()method compare items in the array. A comparison function is passed two values from the array (what you don t see is that the array.sort()method rapidly sends numerous pairs of values from the array to help it sort through all entries). The comparison function lets the sort() method know which of the two items comes before the other, based on the value the function returns. Assuming that the function compares two values, aand b, the returned value reveals information to the sort()method, as shown in Table 37-1. Table 37-1 Comparison Function Return Values Return Value Range Meaning < 0 Value b should sort later than a 0 The order of a and b should not change > 0 Value a should sort later than b Consider the following example: myArray = new Array(12, 5, 200, 80) function compare(a,b) { return a - b } myArray.sort(compare) The array has four numeric values in it. To sort the items in numerical order, you define a comparison function (arbitrarily named compare()), which is called from the sort() method. Note that unlike invoking other functions, the parameter of the sort() method uses a reference to the function, which lacks parentheses. When the compare()function is called, JavaScript automatically sends two parameters to the function in rapid succession until each element has been compared with the others. Every time compare()is called, JavaScript assigns two of the array s values to the parameter variables (aand b). In the preceding example, the returned value is the difference between a and b. If a is larger than b, then a positive value goes back to the sort() method, telling it to sort a later than b (that is, position a at a higher value index position than b). Therefore, bmay end up at myArray[0], whereas a ends up at a higher index-valued location. On the other array.sort()
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1001Chapter 37 .The Array Object On the Example (with Listing 37-8) on the CD-ROM CD-ROM Related Items: array.sort() method. array.slice(startIndex [, endIndex]) Returns: Array. NN2 NN3 NN4 NN6 IE3/J1 IE3/J2 IE4 IE5 IE5.5 Compatibility . . . Behaving as its like-named string method, array.slice()lets you extract a con tiguous series of items from an array. The extracted segment becomes an entirely new array object. Values and objects from the original array have the same kind of behavior as arrays created with the array.concat()method. One parameter is required the starting index point for the extraction. If you don t specify a second parameter, the extraction goes all the way to the end of the array; otherwise the extraction goes to, but does not include, the index value sup plied as the second parameter. For example, extracting Earth s neighbors from an array of planet names looks as the following. var solarSys = new Array( Mercury , Venus , Earth , Mars , Jupiter , Saturn , Uranus , Neptune , Pluto ) var nearby = solarSys.slice(1,4) // result: new array of Venus , Earth , Mars Related Items: array.splice(), string.slice() methods. array.sort([compareFunction]) Returns: Array of entries in the order as determined by the compareFunction algorithm. NN2 NN3 NN4 NN6 IE3/J1 IE3/J2 IE4 IE5 IE5.5 Compatibility . . . JavaScript array sorting is both powerful and a bit complex to script if you haven t had experience with this kind of sorting methodology. The purpose, obviously, is to let your scripts sort entries of an array by almost any kind of criterion that you can associate with an entry. For entries consisting of strings, the criterion may be their alphabetical order or their length; for numeric entries, the criterion may be their numerical order. array.sort()
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1000 Part IV . JavaScript Core Language Reference JavaScript in NN4+ and IE5.5 lets you turn an array into one of these spring- loaded stacks. But instead of placing trays on the pile, you can place any kind of data at either end of the stack, depending on which method you use to do the stacking. Similarly, you can extract an item from either end. Perhaps the most familiar terminology for this is push and pop. When you push() a value onto an array, the value is appended as the last entry in the array. When you issue the array.pop()method, the last item in the array is removed from the stack and is returned, and the array shrinks in length by one. In the follow ing sequence of statements, watch what happens to the value of the array used as a stack: var source = new Array( Homer , Marge , Bart , Lisa , Maggie ) var stack = new Array() // stack = stack.push(source[0]) // stack = Homer stack.push(source[2]) // stack = Homer , Bart var Simpson1 = stack.pop() // stack = Homer ; Simpson1 = Bart var Simpson2 = stack.pop() // stack = ; Simpson2 = Homer While push()and pop() work at the end of an array, another pair of methods works at the front. Their names are not as picturesque as push() and pop(). To insert a value at the front of an array, use the array.unshift() method; to grab the first element and remove it from the array, use array.shift(). Of course, you are not required to use these methods in matching pairs. If you push() a series of values onto the back end of an array, you can shift()them off from the front end without complaint. It all depends on how you need to process the data. Related Items: array.concat(), array.slice() method. array.reverse() Returns: Array of entries in the opposite order of the original. NN2 NN3 NN4 NN6 IE3/J1 IE3/J2 IE4 IE5 IE5.5 Compatibility . . . Occasionally, you may find it more convenient to work with an array of data in reverse order. Although you can concoct repeat loops to count backward through index values, a CGI program on the server may prefer the data in a sequence opposite to the way it was most convenient for you to script it. You can have JavaScript switch the contents of an array for you: Whatever element was last in the array becomes the 0 index item in the array. Bear in mind that if you do this, you re restructuring the original array, not copying it, even though the method also returns a copy of the reversed version. A reload of the document restores the order as written in the HTML document. array.reverse()
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999Chapter 37 .The Array Object array.join(separatorString) Returns: String of entries from the array delimited by the separatorString value. NN2 NN3 NN4 NN6 IE3/J1 IE3/J2 IE4 IE5 IE5.5 Compatibility . . . You cannot view data in an array when it s in that form. Nor can you put an array into a form element for transmittal to a server CGI program. To make the transition from discrete array elements to string, the array.join() method handles what would otherwise be a nasty string manipulation exercise. The sole parameter for this method is a string of one or more characters that you want to act as a delimiter between entries. For example, if you want commas between array items in their text version, the statement is var arrayText = myArray.join( , ) Invoking this method does not change the original array in any way. Therefore, you need to assign the results of this method to another variable or a value property of a form element. On the Example (with Listing 37-7) on the CD-ROM CD-ROM Related Items: string.split() method. array.pop() array.push(valueOrObject) array.shift() array.unshift(valueOrObject) Returns: One array entry value. NN2 NN3 NN4 NN6 IE3/J1 IE3/J2 IE4 IE5 IE5.5 Compatibility . . The notion of a stack is well known to experienced programmers, especially those who know about the inner workings of assembly language at the CPU level. Even if you ve never programmed a stack before, you have encountered the concept in real life many times. The classic analogy is the spring-loaded pile of cafeteria trays. If the pile were created one tray at a time, each tray would be pushed into the stack of trays. When a customer comes along, the topmost tray (the last one to be pushed onto the stack) gets popped off. The last one to be put on the stack is the first one to be taken off. array.pop()
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998 Part IV . JavaScript Core Language Reference When you need to call upon that function (which has essentially become a new temporary method for the Array object), invoke it as you would any object method. Therefore, if an array named CDCollection has been created and a proto type method showCoverImage()has been attached to the array, the call to invoke the method for a tenth listing in the array is CDCollection.showCoverImage(9) where the parameter of the function uses the index value to perhaps retrieve an image whose URL is a property of an object assigned to the 10th item of the array. Array Object Methods After you have information stored in an array, JavaScript provides several meth ods to help you manage that data. These methods, all of which belong to array objects you create, have evolved over time, so observe carefully which browser versions a desired method works with. array.concat(array2) Returns: array Object. NN2 NN3 NN4 NN6 IE3/J1 IE3/J2 IE4 IE5 IE5.5 Compatibility . . . The array.concat() method allows you to join two array objects into a new, third array object. The action of concatenating the arrays does not alter the contents or behavior of the two original arrays. To join the arrays, you refer to the first array object to the left of the period before the method; a reference to the second array is the parameter to the method. For example: var array1 = new Array(1,2,3) var array2 = new Array( a , b , c ) var array3 = array1.concat(array2) // result: array with values 1,2,3, a , b , c If an array element is a string or number value (not a string or number object), the values are copied from the original arrays into the new one. All connection with the original arrays ceases for those items. But if an original array element is a reference to an object of any kind, JavaScript copies a reference from the original array s entry into the new array. So if you make a change to either array s entry, the change occurs to the object, and both array entries reflect the change to the object. On the CD-ROM Example (with Figure 37-1 and Listing 37-6) on the CD-ROM Related Items: array.join() method. array.concat()
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997Chapter 37 .The Array Object Inside JavaScript, an array object has its dictionary definition of methods and length property items that all array objects have in common. The prototype property enables your scripts to ascribe additional properties or methods that apply to all the arrays you create in the currently loaded documents. You can override this prototype, however, for any individual objects as you want. To demonstrate how the prototype property works, Listing 37-5 creates a prototype property for all array objects generated from the static Array object. As the script generates new arrays (instances of the Arrayobject, just as a date object is an instance of the Date object), the property automatically becomes a part of those arrays. In one array, c, you override the value of the prototype sponsor property. By changing the value for that one object, you don t alter the value of the prototype for the Array object. Therefore, another array created afterward, d, still gets the original sponsor property value. Listing 37-5: Adding a prototype Property

You can assign properties and functions to a prototype. To assign a function, define the function as you normally would in JavaScript. Then assign the function to the prototypeby name: function newFunc(param1) { // statements } Array.prototype.newMethod = newFunc // omit parentheses in this reference Array.prototype
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996 Part IV . JavaScript Core Language Reference or, for the extreme of unreadable brevity with literal notation: // create new main array var regionalOffices = [ [ New York , Shirley Smith , 300000], [ Chicago , Todd Gaston , 250000], [ Houston , Leslie Jones , 350000], [ Portland , Harold Zoot , 225000] ] Accessing a single data point of an array of arrays requires a double array refer ence. For example, retrieving the manager s name for the Houston office requires the following syntax: var HoustonMgr = regionalOffices[2][1] The first index in brackets is for the outermost array (regionalOffices); the second index in brackets points to the item of the array returned by regionalOffices[2]. Array Object Properties constructor See string.constructor (Chapter 34). length Value: Integer Read/Write NN2 NN3 NN4 NN6 IE3/J1 IE3/J2 IE4 IE5 IE5.5 Compatibility . . . A true array object s lengthproperty reflects the number of entries in the array. An entry can be any kind of JavaScript value, including null. If an entry is in the 10th cell and the rest are null, the length of that array is 10. Note that because array index values are zero-based, the index of the last cell of an array is one less than the length. This characteristic makes it convenient to use the property as an automatic counter to append a new item to an array: myArray[myArray.length] = valueOfAppendedItem Thus, a generic function does not have to know which specific index value to apply to an additional item in the array. prototype Value: Variable or Function Read/Write NN2 NN3 NN4 NN6 IE3/J1 IE3/J2 IE4 IE5 IE5.5 Compatibility . . . Array.prototype
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