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.. » JavaScript » Introduction » Array Object - Properties
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Array Object - Properties

From previous pages, you have learnt that JavaScript arrays have an object. We will discuss about that object in this page. Arrays can directly be created from the object,
var arr = new Array(1, "Hello World", true);
Nevertheless, It is best to create arrays using the explicit method e.g var arr = [1, "Hello World", true];. The array object have various properties and methods that can be used in manipulating all JavaScript arrays whether created from the arrays' object or using the explicit method of creating arrays. In this page, we shall get familiarized with some of these properties and methods. Properties 1. length The length property of an array returns the number of individual values contained in an array.
var myArray = [1, 2, 3, 4];

var len = myArray.length; //The length of the array
alert(len); //4


2. prototype The prototype property is a static property that allows you to add new properties or methods to the prototype from which every array object is created. By doing this, you can define new properties and methods every created array object will have in a document or script.
//Adding a new property... The object of every array will have this property just as they have the length property
Array.prototype.isArray = true;

//A function to check if variable or value is an array
function isArray(arr){
if (arr !== undefined && arr.isArray !== undefined && arr.isArray == true)
return "Array";
return false;

var array = [1,3,5];
alert(isArray(array)); //Array
alert(isArray([])); //Array
alert(isArray("Hello World")); //Not Array


Above, we wanted to define a function to know if a variable is an array or not. So, first, we added a new property(isArray) whose value is true to the prototype used in creating arrays' object. This ensures that whenever an array is created, its object also have this property. Now, whenever a value is passed to the function, the function checks to know if the value has this new property and whether the value is equal to true. If true, it is an array. 3. constructor This property contains the function used in defining the prototype from which an array object is created. Since, the Array prototype was predefined i.e it was defined in JavaScript by default and not by you, there is a limit to what you can see.
var arr = ["Hello World"];


Check next page for the Array object methods. SUMMARY
  1. All JavaScript arrays whether created explicitly or implicitly has an object containing properties and methods.
  2. The length property enables you to know the number of values in an array.
  3. The prototype property just like every object's prototype property enables you to modify the prototype used in creating objects for arrays. You can then add or modify properties and methods of the array prototype so that every array object possesses these changes.
  4. The constructor property returns the object constructor that was used in defining the prototype for creating arrays' objects.
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