Variable data types

JavaScript supports various types of data that can be assigned to your variables. Unlike other strongly typed languages such as .NET or C++, JavaScript is a loosely typed language. What this means is that you don't have to specify the type of data that will occupy your variable. The JavaScript interpreter does this for you on the fly. You can assign strings of text, numbers, Boolean true/false values, arrays, or objects to your variables.

Numbers and strings are pretty straight forward for the most part. Strings are simply text enclosed by either a single or a double quote. For instance:

var baseMapLayer = "Terrain";
var operationalLayer = 'Parcels';

Numbers are not enclosed inside quote marks and can be integers or floating point numbers:

var currentMonth = 12;
var layered = 3;
var speed = 34.35;

One thing we would point out to new programmers is that numeric values can be assigned to string variables through the use of single or double quotes that enclose the value. This can be confusing at times for some new programmers. For instance, a value of 3.14 without single or double-quotes is a numeric data type while a value of "3.14" with single or double quotes is assigned a string data type.

Other data types include Booleans that are simply true or false values, and arrays that are a collection of data values. An array basically serves as a container for multiple values. For instance, you could store a list of geographic data layer names within an array and access each element in the array individually as required.

Arrays allow you to store multiple values in a single variable. For example, you might want to store the names of all the layers you want to add to a map. Rather than creating individual variables for each layer you could use an array to store all of them in a single variable. You can then reference individual values from the array using an index number, or by looping through them with a for loop. The following code example shows how to create an array in JavaScript and reference its individual members via their index values:

var myLayers=new Array();  
myLayers[0]="Parcels";        
myLayers[1]="Streets"; 
myLayers[2]="Streams"; 

You could also simplify the creation of this array variable as seen in the following code example where the array has been created as a comma-separated list enclosed in brackets:

var myLayers = ["Parcels", "Streets", "Streams"]; 

Bear in mind that if you access array elements via their index, the index numbering is zero-based. This means that the first item in the array occupies position 0 and each successive item in the array is incremented by one:

var layerName = myLayers[0]; //returns Parcels