JavaScript Arrays
An Array is an object type designed for storing data collections.
Key characteristics of JavaScript arrays are:
Elements: An array is a list of values, known as elements.
Ordered: Array elements are ordered based on their index.
Zero indexed: The first element is at index 0, the second at index 1, and so on.
Dynamic size: Arrays can grow or shrink as elements are added or removed.
Heterogeneous: Arrays can store elements of different data types (numbers, strings, objects and other arrays).
Why Use Arrays?
If you have a list of items (a list of car names, for example), storing the names in single variables could look like this:
let car1 = "Saab";
let car2 = "Volvo";
let car3 = "BMW";
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.
Creating an Array
Using an array literal is the easiest way to create a JavaScript Array.
Syntax:
const array_name = [item1, item2, ...];
It is a common practice to declare arrays with the const keyword.
Learn more about const with arrays in the chapter: JS Array Const.
Using the JavaScript Keyword new
The following example also creates an Array, and assigns values to it:
Example
const cars = new Array("Saab", "Volvo", "BMW");
The two examples above do exactly the same.
There is no need to use new Array().
For simplicity, readability and execution speed, use the array literal method.
Arrays are Objects
Arrays are a special type of objects. The type of 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:
Array:
const person = ["John", "Doe", 46];
Array Elements Can Be Objects
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:
myArray[0] = Date.now;
myArray[1] = myFunction;
myArray[2] = myCars;
The length Property
The length property of an array returns the length of an array (the number of array elements).
Example
const fruits = ["Banana", "Orange", "Apple", "Mango"];
let length = fruits.length;
The length property is always one more than the highest array index.
Accessing the First Array Element
Example
const fruits = ["Banana", "Orange", "Apple", "Mango"];
let fruit = fruits[0];
Accessing the Last Array Element
Example
const fruits = ["Banana", "Orange", "Apple", "Mango"];
let fruit = fruits[fruits.length - 1];
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