Arrays

Array stores multiple values.

Initialization

There are couple of ways to initialize array:

Empty array

let arrayName = [];

Initial values

let colors = ["red", "green", "blue"];

In this example an array with 3 elements is created.

Size

Size is the count of elements in array.

It's accessed via the length property.

let prices = [15, 20, 30]; console.log(prices.length);

Output:

3

Accessing values

Array's values can be accessed via indexes starting from 0.

If we declare the following array:

let scores = [ 60, 78, 95, 88 ];

It's elements are:

So if we type the following line:

console.log(scores[0] + ' ' + scores[1]);

It will print:

60 78

Index out of Bounds

Accessing index outside of the array results in undefined value

Let's have an array with 4 elements. If we access the 4th or higher index undefined will be returned.

Such example is:

let scores = [ 60, 78, 95, 88 ]; console.log(scores[4]);

Output:

undefined

Printing All Elements

Let's have an example in which all elements of array are printed.

let scores = [60, 78, 95, 88]; for(let i = 0; i < scores.length; i++) { console.log(scores[i]); }

Output:

60 78 95 88

Other way to do it is via the forEach.

let scores = [60, 78, 95, 88]; scores.forEach(function(score) { console.log(score); });

Notice that forEach is not supported by the older browsers such as Internet Explorer.

Inserting Elements

Elements can be inserted using the push function.

Let's have a program which fills array with values:

let ages = []; ages.push(15); ages.push(25); ages.push(28);

Product Of Elements

Let's have a program which calculates the product of all even numbers:

let numbers = [2,3,4,5]; let multiplication = 1; numbers.forEach(function(num) { if(num % 2 === 0) { // If number is even. multiplication *= num; } }); console.log(multiplication);

Output:

8

The only even numbers in the array are 2 and 4 which are multiplied.