Dylan  Iqbal

Dylan Iqbal


JavaScript Basics: Arrays and Loops

This lesson covers the basics of JavaScript, the language that provides interactivity on the web. In this lesson, you'll learn about arrays and loops, which are used to manipulate data.


Working with data is a common task for any language, and it's a much easier task when data is organized in a structural format, such as arrays. With arrays, data is stored in a structure similar to a list. One major benefit of arrays is that you can store different types of data in one array.

Arrays are all around us! Can you think of a real-life example of an array, such as a solar panel array?

The syntax for an array is a pair of square brackets.

let myArray = [];

This is an empty array, but arrays can be declared already populated with data. Multiple values in an array are separated by a comma.

let iceCreamFlavors = ["Chocolate", "Strawberry", "Vanilla", "Pistachio", "Rocky Road"];

The array values are assigned a unique value called the index, a whole number that is assigned based on its distance from the beginning of the array. In the example above, the string value "Chocolate" has an index of 0, and the index of "Rocky Road" is 4. Use the index with square brackets to retrieve, change, or insert array values.

Does it surprise you that arrays start at the zero index? In some programming languages, indexes start at 1. There's an interesting history around this, which you can read on Wikipedia.

let iceCreamFlavors = ["Chocolate", "Strawberry", "Vanilla", "Pistachio", "Rocky Road"];
iceCreamFlavors[2]; //"Vanilla"

You can leverage the index to change a value, like this:

iceCreamFlavors[4] = "Butter Pecan"; //Changed "Rocky Road" to "Butter Pecan"

And you can insert a new value at a given index like this:

iceCreamFlavors[5] = "Cookie Dough"; //Added "Cookie Dough"

A more common way to push values to an array is by using array operators such as array.push()

To find out how many items are in an array, use the length property.

let iceCreamFlavors = ["Chocolate", "Strawberry", "Vanilla", "Pistachio", "Rocky Road"];
iceCreamFlavors.length; //5

Try it yourself! Use your browser's console to create and manipulate an array of your own creation.


Loops allow for repetitive or iterative tasks, and can save a lot of time and code. Each iteration can vary in their variables, values, and conditions. There are different types of loops in JavaScript, and they have small differences, but essentially do the same thing: loop over data.

For Loop

The for loop requires 3 parts to iterate: - counter A variable that is typically initialized with a number that counts the number of iterations. - condition Expression that uses comparison operators to cause the loop to stop when true - iteration-expression Runs at the end of each iteration, typically used to change the counter value

    //Counting up to 10
    for (let i = 0; i < 10; i++) {

Run this code in a browser console. What happens when you make small changes to the counter, condition, or iteration expression? Can you make it run backwards, creating a countdown?

While loop

Unlike the syntax for the for loop, while loops only require a condition that will stop the loop when true. Conditions in loops usually rely on other values like counters, and must be managed during the loop. Starting values for counters must be created outside the loop, and any expressions to meet a condition, including changing the counter must be maintained inside the loop.

//Counting up to 10
let i = 0;
while (i < 10) {

Why would you choose a for loop vs. a while loop? 17K viewers had the same question on StackOverflow, and some of the opinions might be interesting to you.

Loops and Arrays

Arrays are often used with loops because most conditions require the length of the array to stop the loop, and the index can also be the counter value.

let iceCreamFlavors = ["Chocolate", "Strawberry", "Vanilla", "Pistachio", "Rocky Road"];

for (let i = 0; i < iceCreamFlavors.length; i++) {
} //Ends when all flavors are printed

Experiment with looping over an array of your own making in your browser's console.


There are other ways of looping over arrays other than for and while loops. There are forEach, for-of, and map. Rewrite your array loop using one of these techniques.

Post-Lecture Quiz

Post-lecture quiz

Review & Self Study

Arrays in JavaScript have many methods attached to them, extremely useful for data manipulation. Read up on these methods and try some of them out (like push, pop, slice and splice) on an array of your creation.


Loop an Array

Originally published at https://github.com/microsoft/Web-Dev-For-Beginners/blob/main/2-js-basics/4-arrays-loops/README.md 


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JavaScript Basics: Arrays and Loops
Lowa Alice

Lowa Alice


JavaScript Loops Tutorial

JavaScript loops made simple.

📺 The video in this post was made by Programming with Mosh
The origin of the article: https://www.youtube.com/watch?v=s9wW2PpJsmQ&list=PLTjRvDozrdlxEIuOBZkMAK5uiqp8rHUax&index=8
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#javascript #loops #javascript loops #javascript loops tutorial

Lowa Alice

Lowa Alice


JavaScript Arrays Tutorial. DO NOT MISS!!!

Learn JavaScript Arrays

📺 The video in this post was made by Programming with Mosh
The origin of the article: https://www.youtube.com/watch?v=oigfaZ5ApsM&list=PLTjRvDozrdlxEIuOBZkMAK5uiqp8rHUax&index=4
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Thanks for visiting and watching! Please don’t forget to leave a like, comment and share!

#arrays #javascript #javascript arrays #javascript arrays tutorial

Alverta  Crist

Alverta Crist


How To Loop Through An Array In JavaScript

The easiest way to use for loop and forEach array method.

#javascript #javascript array #looping array #morioh

Terry  Tremblay

Terry Tremblay


Fill and Filter in Array in JavaScript

By the word Array methods, I mean the inbuilt array functions, which might be helpful for us in so many ways. So why not just explore and make use of them, to boost our productivity.

Let’s see them together one by one with some amazing examples.


The _fill()_ method changes all elements in an array to a static value, from a start index (default _0_) to an end index (default _array.length_). It returns the modified array.

In simple words, it’s gonna fill the elements of the array with whatever sets of params, you pass in it. Mostly we pass three params, each param stands with some meaning. The first param value: what value you want to fill, second value: start range of index(inclusive), and third value: end range of index(exclusive). Imagine you are going to apply this method on some date, so that how its gonna look like eg: array.fill(‘Some date’, start date, end date).

NOTE: Start range is inclusive and end range is exclusive.

Let’s understand this in the below example-

//declare array
var testArray = [2,4,6,8,10,12,14];


When you run this code, you gonna see all the elements of testArray will be replaced by 'A' like [“A”,"A","A","A","A","A","A"].

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Introduction With Basic JavaScript

The world’s most misunderstood programming language is JavaScript but JavaScript is now used by an incredible number of high-profile applications. So, it’s an important skill for any web or mobile developer to enrich the deeper knowledge in it.

Unlike most programming languages, the JavaScript language has no concept of input or output. It is designed to run as a scripting language in a host environment, and it is up to the host environment to provide mechanisms for communicating with the outside world.

Its syntax is based on the Java and C languages — many structures from those languages apply to JavaScript as well. JavaScript supports object-oriented programming with object prototypes, instead of classes. JavaScript also supports functional programming — because they are objects, functions may be stored in variables and passed around like any other object.

Let’s start off by looking at the building blocks of any language: the types. JavaScript programs manipulate values, and those values all belong to a type. JavaScript’s types are:

· Number

· String

· Boolean

· Function

· Object

· Symbol

and undefined and null, which are … slightly odd. And Array, which is a special kind of object. Date and RegExp, which are objects that you get for free. And to be technically accurate, functions are just a special type of object. So the type of diagram looks like this:

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