Javascript Arrays

, 25/09/2017

JavaScript arrays are used to store multiple values in a single variable.

var cars = ["Saab", "Volvo", "BMW"];

What is it ?

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:

var car1 = "Saab";
var car2 = "Volvo";
var 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.

var cars = ["Saab", "Volvo", "BMW"];

Access the Elements of an Array

You refer to an array element by referring to the index number. This statement accesses the value of the first element in cars:

var name = cars[0];

This statement modifies the first element in cars:

cars[0] = "Opel"; 

Example

var cars = ["Saab", "Volvo", "BMW"];
document.getElementById("demo").innerHTML = cars[0]; 

Nb : [0] is the first element in an array. [1] is the second. Array indexes start with 0.

The full array can be accessed by referring to the array name:

var cars = ["Saab", "Volvo", "BMW"];
document.getElementById("demo").innerHTML = cars;

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;

Arrays manipulation

Get the length of an array :

var fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.length;  // the length of fruits is 4 

Looping Array Elements

var fruits, text, fLen, i;

fruits = ["Banana", "Orange", "Apple", "Mango"];
fLen = fruits.length;
text = "
    "; for (i = 0; i < fLen; i++) { text += "
  • " + fruits[i] + "
  • "; }

Adding Array Elements

var fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.push("Lemon");                // adds a new element (Lemon) to fruits 

The Difference Between Arrays and Objects

In JavaScript, arrays use numbered indexes.

In JavaScript, objects use named indexes.

When to Use Arrays. When to use Objects.

  • JavaScript does not support associative arrays.
  • You should use objects when you want the element names to be strings (text).
  • You should use arrays when you want the element names to be numbers.

Content from https://www.w3schools.com/js/js_arrays.asp