Summary  
This chapter demonstrates how to use loops—particularly for loops—to iterate through arrays by index using the length property, enabling printing each element and performing bulk updates on array values.

General domain of usage  
Data processing

Loops enable us to efficiently go through all or specific elements of an array.

For example, we can use a for loop to iterate through all elements of an array and output them:

let numbers = [1, 1, 2, 3, 5, 8, 13, 21];

for(let i = 0; i < numbers.length; i++) {
  console.log("Element " + (i + 1) + " of the array is: " + numbers[i]);
}

This is especially useful when we need to perform an operation on multiple elements in an array:

let numbers = [1, 1, 2, 3, 5, 8, 13, 21];

console.log("Before:", numbers);
for(let i = 0; i < numbers.length; i++) {
  numbers[i] *= 2;
}
console.log("After:", numbers);

We can use a `while` or a `do-while` loop for this purpose as well, however, that is not the convention. 

let numbers = [1, 1, 2, 3, 5, 8, 13, 21];

console.log("Before:", numbers);
let i = 0;
while(i < numbers.length) {
  numbers[i] *= 2;
  i += 1;
}
console.log("After:", numbers);

Even though the same results can be achieved using `while` or `do-while` loops, it is recommended to use a `for` loop when iterating through arrays because it is the conventional and more readable approach.

Does the following code modify the original array?

Dive into the world of the most popular language for front-end development – JavaScript. JavaScript is a language built into almost every browser and can be used for a wide variety of tasks. Learn the basic functionality and prepare yourself for the challenges and more advanced programming techniques.

An introduction to JavaScript, covering the basic syntax of the language along with key terms and concepts that form the foundation for learning advanced features. The section includes hands-on tasks designed to help practice these concepts and make the content easy to remember without effort.

Learn how to store data and retrieve it later using variables. Additionally, explore basic data types and understand how they interact with each other.

Learn how to write expressions that evaluate to "true" or "false" based on conditions, such as "Is X equal to Y?". This will be followed by an exploration of conditional statements that allow the conditional execution of specific lines of code.

A powerful programming feature called a function allows the execution of a block of code multiple times with minimal repetition. The section introduces core concepts and syntax for defining and using functions effectively.


The concept of Arrays is introduced as a way to organize and manage collections of data. The material covers how arrays structure data and enable efficient operations on multiple values.


Loops are a fundamental feature in programming used to reduce redundancy and handle repetitive tasks efficiently. The content covers the three main types of loops in JavaScript, their syntax, use cases, and how they can be combined with arrays to streamline operations and improve performance.

Using Loops with Arrays

1. What does the following code output?

2. Does the following code modify the original array?

Awesome!

Using Loops with Arrays

1. What does the following code output?

2. Does the following code modify the original array?