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JavaScript arrays are used to store multiple values in a single variable.
An array is a special variable, which can hold more than one value at a time.
If you have a list of items (a list of car names, for example), storing the cars in single variables could look like this:
However, what if you want to loop through the cars and find a specific one? And what if you had not 3 cars, but 300?
The solution is an array!
An array can hold many values under a single name, and you can access the values by referring to an index number.
Using an array literal is the easiest way to create a JavaScript Array.
Syntax:
Spaces and line breaks are not important. A declaration can span multiple lines:
The following example also creates an Array, and assigns values to it:
The two examples above do exactly the same. There is no need to use new Array()
.
For simplicity, readability and execution speed, use the first one (the array literal method).
You access an array element by referring to the index number.
This statement accesses the value of the first element in cars
:
Note: Array indexes start with 0.
[0] is the first element. [1] is the second element.
This statement changes the value of the first element in cars
:
With JavaScript, the full array can be accessed by referring to the array name:
Arrays are a special type of objects. The typeof
operator in JavaScript returns 'object' for arrays.
But, JavaScript arrays are best described as arrays.
Arrays use numbers to access its 'elements'. In this example, person[0]
returns John:
Objects use names to access its 'members'. In this example, person.firstName
returns John:
Key generator program free download. JavaScript variables can be objects. Arrays are special kinds of objects.
Because of this, you can have variables of different types in the same Array.
You can have objects in an Array. You can have functions in an Array. You can have arrays in an Array:
The real strength of JavaScript arrays are the built-in array properties and methods:
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Array methods are covered in the next chapters.
The length
property of an array returns the length of an array (the number of array elements).
The length
property is always one more than the highest array index.
The safest way to loop through an array, is using a for
loop:
You can also use the Array.forEach()
function:
The easiest way to add a new element to an array is using the push()
method:
New element can also be added to an array using the length
property:
WARNING !
Adding elements with high indexes can create undefined 'holes' in an array:
Many programming languages support arrays with named indexes.
Arrays with named indexes are called associative arrays (or hashes).
JavaScript does not support arrays with named indexes.
In JavaScript, arrays always use numbered indexes.
WARNING !!
If you use named indexes, JavaScript will redefine the array to a standard object.
After that, some array methods and properties will produce incorrect results.
In JavaScript, arrays use numbered indexes.
In JavaScript, objects use named indexes.
Arrays are a special kind of objects, with numbered indexes.
There is no need to use the JavaScript's built-in array constructor new
Array().
Use []
instead.
These two different statements both create a new empty array named points:
These two different statements both create a new array containing 6 numbers:
The new
keyword only complicates the code. It can also produce some unexpected results:
What if I remove one of the elements?
A common question is: How do I know if a variable is an array?
The problem is that the JavaScript operator typeof
returns 'object
':
The typeof operator returns object because a JavaScript array is an object.
To solve this problem ECMAScript 5 defines a new method Array.isArray()
:
The problem with this solution is that ECMAScript 5 is not supported in older browsers.
To solve this problem you can create your own isArray()
function:
The function above always returns true if the argument is an array.
Or more precisely: it returns true if the object prototype contains the word 'Array'.
The instanceof
operator returns true if an object is created by a given constructor: