Impara What Are Arrays?

Definition

An array is simply an ordered collection of variables.

Defining an Array

The general syntax of defining an array is:

let arrayName = [ element1, element2, … ];

We can declare an empty array as well:

let arrayName = [];

Arrays are useful when we need to store multiple values in a single variable instead of creating separate variables for each value.

This makes data easier to organize and manipulate. For example, we can store the names of the class students in an array:

We can output all the elements of an array by simply using it's name in a console.log statement:


              12345
            
let students = [ "Emma", "Alex", "Chris" ];
console.log(students);

let emptyArray = [];
console.log(emptyArray);

Indexing

We can access an element at a specific position in the array by indexing.

The syntax for indexing is:

arrayName[index]

Here arrayName is the name of the array, and index refers to the position of the element in the array.

The index values start from 0, which means the first element always has an index 0.


              1234
            
let students = [ "Emma", "Alex", "Chris" ];
console.log(students[0]); // Output: Emma
console.log(students[1]); // Output: Alex
console.log(students[2]); // Output: Chris

Using an invalid index returns undefined:


              123
            
let students = [ "Emma", "Alex", "Chris" ];
console.log(students[-1]); // Output: undefined
console.log(students[4]); // Output: undefined

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Sezione 1. Capitolo 56

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Definition

An array is simply an ordered collection of variables.

Defining an Array

The general syntax of defining an array is:

let arrayName = [ element1, element2, … ];

We can declare an empty array as well:

let arrayName = [];

Arrays are useful when we need to store multiple values in a single variable instead of creating separate variables for each value.

This makes data easier to organize and manipulate. For example, we can store the names of the class students in an array:

We can output all the elements of an array by simply using it's name in a console.log statement:


              12345
            
let students = [ "Emma", "Alex", "Chris" ];
console.log(students);

let emptyArray = [];
console.log(emptyArray);

Indexing

We can access an element at a specific position in the array by indexing.

The syntax for indexing is:

arrayName[index]

Here arrayName is the name of the array, and index refers to the position of the element in the array.

The index values start from 0, which means the first element always has an index 0.


              1234
            
let students = [ "Emma", "Alex", "Chris" ];
console.log(students[0]); // Output: Emma
console.log(students[1]); // Output: Alex
console.log(students[2]); // Output: Chris

Using an invalid index returns undefined:


              123
            
let students = [ "Emma", "Alex", "Chris" ];
console.log(students[-1]); // Output: undefined
console.log(students[4]); // Output: undefined

Tutto è chiaro?

Grazie per i tuoi commenti!

Sezione 1. Capitolo 56

What Are Arrays?

Defining an Array

Indexing

1. What is an array in JavaScript?

2. Which of the following is the correct way to declare an array?

3. What does the following code output?

4. What will be the output of the following code?

What Are Arrays?

Defining an Array

Indexing

1. What is an array in JavaScript?

2. Which of the following is the correct way to declare an array?

3. What does the following code output?

4. What will be the output of the following code?