The Array class The Array literal in Java

Generator QR Code in Java The Array class The Array literal

Unfortunately, there is a little inconsistency between the official specifications and the way each of the major browser manufacturers has implemented arrays in JavaScript In this chapter, we will examine how arrays are created and how to create code that works across all browsers We will also take a look at some of the exciting improvements in arrays in JavaScript 20

There are three ways to create an Array using the JavaScript Array class:

new Array () new Array (size) new Array (element1, element2, , elementN)

Passing no arguments to the constructor of the Array class creates an empty array, also called an array of zero length (In JavaScript, the number of items inside an array is known as its length) We can then populate the array manually, as follows 1 We start by defining a variable to contain our array

var months;

var months = new Array();

var months = new Array(); months[0] = "January";

var months = new Array(); months[0] = "January"; months[1] = "February"; months[2] = "March"; months[3] = "April"; months[4] = "May"; months[5] = "June"; months[6] = "July"; months[7] = "August"; months[8] = "September"; months[9] = "October"; months[10] = "November"; months[11] = "December";

5 We now have an array that can be accessed by the rest of our program using only its numerical index

var months = new Array(); months[0] = "January"; months[1] = "February"; months[2] = "March"; months[3] = "April"; months[4] = "May"; months[5] = "June"; months[6] = "July"; months[7] = "August"; months[8] = "September"; months[9] = "October"; months[10] = "November"; months[11] = "December"; for (var i = 0; i < 12; i++) { documentwrite (months[i] + "<br>"); }

6 As you can see here, JavaScript is able to store a list of related values (months of the year) into a single variable, and then easily access each of those values for later use

7 A list such as this (months of the year) is convenient if you want your program to convert a numerical month into its string equivalent Luckily, the Date object s getMonth() function returns the month in a range of 0 to 11, so we do not even have to adjust the value before using it

var today = new Date(); var monthnum = todaygetMonth(); documentwrite ("Today is a lovely " + months[monthnum] + " day");

JavaScript allows you to specify an initial length for your array by passing a single integer as a parameter

var months = new Array(12);

Setting the length of an array in advance like this provides few advantages in JavaScript 15, since arrays grow automatically Perhaps the one benefit it does provide is to remind you how large an array you intended to define The length of an array can also be set within the program by altering the length property of the Array object

var months = new Array(); monthslength = 12;

Looking at the months array defined earlier, we ended up writing 13 lines of code just to create and initialize the array It would be nice if we could create this same array using only one line of code Of course, I wouldn t have mentioned it if JavaScript couldn t do it

var months = new Array ("January", "February", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December");

The constructor of the Array class also accepts a comma-separated list of the initial values of the array The first item listed is assigned the index 0, the next item becomes index 1, and so on This is especially helpful for long lists of items For instance, if we needed an array containing the 50 US states, it would be much easier to create it in one line of code, as opposed to 51 or more

var USStates = new Array ("Alabama", "Alaska", "Arizona", "Arkansas", "California", "Colorado", "Connecticut", "Delaware", "Florida", "Georgia", "Hawaii", "Idaho", "Illinois", "Indiana", "Iowa", "Kansas", "Kentucky", "Louisiana", "Maine", "Maryland", "Massachusetts", "Michigan", "Minnesota", "Mississippi", "Missouri", "Montana", "Nebraska", "Nevada", "New Hampshire", "New Jersey", "New Mexico", "New York", "North Carolina", "North Dakota", "Ohio", "Oklahoma", "Oregon", "Pennsylvania", "Rhode Island", "South Carolina", "South Dakota", "Tennessee", "Texas", "Utah", "Vermont", "Virginia", "Washington", "West Virginia", "Wisconsin", "Wyoming");