While Loops in JavaScript

A while loop is more versatile than a for loop.

A while loop just needs a condition to keep running.

Creating a while loop

  • Add a condition.

for example

while ((rep<=10)

Run the look while the “rep” value is less than or equal to 10

  • Add the staring condition:

let rep = 1;

  • add the code to be executed:

console.log(‘lifting weights repetition ${rep}

  • Add the counter:


let rep=1;
while (rep <=10) {
console.log('lifting weights repetition ${rep});

While Loop doesn’t need a counter

Random variable – throwing a dice until we throw a 6

We don’t know how many times the dice has to be thrown, so we don’t need a counter

let dice = Math.trunc(Math.random() x 6) + 1;

while (dice !==6) {
console.log('Your rolled a ${dice}');

while (dice !==6) is the condition – roll the dice whilst the condition is not equal to 6

JavaScript – the for Loop [2023] for beginners/dummies/SEO-helmets

A for loop, is a loop that will loop through (go through) the elements in an array or the properties of an Object.

You can use it to update arrays, count the number of elements etc

Loops can execute a block of code several times.

With arrays, it’s common(ish) to run the same code over with a different value.

Image source

screenshot source

For Loops tend to be used with arrays (I think!)

The code below the array in the screenshot below, starting with “for”, loops through the variable called “names” above it.
Once it loops through it create “name” and then “console.log(name);” will get it to print on the console.log screen

  • console.log just provides a way of testing and outputting stuff using web developer tools, inspect element etc.

The code below, will do the same as above, but this time it will add “Hello there” before each of the names:

You can also add if conditions. For example, in the code below, the loop will check if “Maria” is in the list, and if so, will print out “Maria is in my list”

You can get the loop to stop once it finds “Maria” by using the “break” keyword.

The above code will print “Ed, John and then Maria and “Maria is in my list”. It will then stop and it won’t print all the names up to “Potter”.

As well as using the for loop with arrays, you can also use it with a single variable like “age”, and add an incremented – for example “age++”

The code shown below will print out and loop 10 times. starting at 0, and then 1, 2 etc. until finally the condition age <10 is no longer met

When the age is 10, it will stop.

A web dev example

Get all the links on a page, and return the number of the links on the page.

When the loop gets to the 6th link, it is no longer less than links.length, and so the loop stops:

(you can click the image to see a lager version, the important code is :

for (i = 0; i < links.length; i++)

To print out the final link, change “<links.length” to “<= links.length” – meaning “less than or equal to links.length”

for (i = 0; i <= links.length; i++)

For In Loops

For in loops, are the same as for loops except they are shorter to write but less flexible.

For Loop Example with an Array

Work out the age of people, given an array with their year of birth in it.

start with the array and then a new array, which will hold the ages:

const years = [1991, 2007, 1969, 2020]
const ages = [];

for(let I = 0; I <years.length; i++) {

ages.push (2023 – years [i] );



the “ages.push” code, will psh the results into the ages array

Continue & Break Statements

Continue is to exit the current iteration and move to the next one

Break will exit completely.

You can use with an if statement

continue loop statement

If the type of the current element, is not a string, then continue.

This will skip any elements/values that are not strings. Continue will exit the current iteration and not print to the console.log

Using break, will terminate the loop completely.

break loop statement

What are objects in Javascript? [2023]

Notes taken from the Udemy Course – the Complete JavaScript Course which you can enroll on here.

I’ve also robbed some screenshots from other sites, but linked to them in the “source”.

  • An object is a collection of properties
  • A property is an association between a name (key) and a value
  • A property’s value can be a function (but then it’s called a “method” for some reason)


Objects provide a way to group values together in an organised fashion.

Objects can store lots of different types of data.

Objects can contain variables, functions or both.Variables found in objects are properties, while functions are methods.

In objects we define key-value pairs. The key is also called the “property name”.

Objects are normally declared within culry braces:

firstName is a “key” and the “value” is “Jonas”.

The name and the value, create a “key value pair”.

There are many ways of creating objects in JavaScript.

Using curly braces is called the “object literal syntax” because you’re writing down the literal object.

The order you write down objects doesn’t matter, unlike in arrays.

How do we get data from an object?

Dot Notation

Screenshot source

The first way to access data in an object is to use “dot notation”:

Dot notation is the most popular method to access the properties of an object.

let obj = {
  boxer: 'jab',
  muayThai: 'kick'
let strike = obj.boxer;
// jab

The dot notation in the example above is – let strike = obj.boxer;

Specify the name of the object, then add a dot, followed by the property name.

The syntax is objectName.propertyName;


Bracket Notation

let obj = {
  boxer: 'jab',
  muaythai: 'kick'
let strike = obj['boxer'];
// jab

You can read a much better article about dot and bracket notation – here –> codeburst.io or here —> plainenglish.io

How do you create objects?

It is a common practice to declare objects with the const keyword.

There are two methods by which you can create an object: an object literal and the object constructor. 


let’s create an object named myCup and give it properties named color, volume, and weight as follows:

let myCup = new Object();
myCup.color = "transparent";
myCup.volume = 1;
myCup.weight = 0.5;

We can write the same object in a shorter notation. Comma-delimited list of  pairs of property names and associated values, enclosed in curly braces:

let myCup = {
 color: "transparent",
 volume: 1,
 weight: 0.5

Above, we declare a variable in the same way with: let myCup equals and then curly brace.


If you are making multiple objects, it’s best to use the object constructor.

You can use a constructor to create a new object by calling the constructor with the new keyword. The new keyword will create an instance of an object and bind the this keyword to the new object.

The this keyword is a reference to the object itself.

function Fighter(name, age, nationality) { 
    this.name = name; 
    this.age = age; 
    this.nationality = nationality; 
    this.bio = function () { 
        console.log(`My name is ${this.name}. I'm ${this.age} years old. I'm from ${this.nationality}`) 

const oladele = new Profile("Izzy", 29, "Nigeria" );
console.log(oladele.bio()); //My name is Izzy. I'm 29 years old. I'm from Nigeria

More info about constructors at Freecodecamp.org

Here’s another example, using the this keyword from w3schools

// Constructor function for Person objects
function Person(first, last, age, eye) {
  this.firstName = first;
  this.lastName = last;
  this.age = age;
  this.eyeColor = eye;

// Create a Person object
const myFather = new Person("John", "Doe", 50, "blue");

// Display age
document.getElementById("demo").innerHTML =
"My father is " + myFather.age + "."; 

The above code gives the output “my father is 50”. (which is printed to the paragraph with the id of “demo”)

Adding a method to an object

We can add a method simply by adding another property that is a function. This function will be able to read the values of the object and work with them.

We will add an example that will print out the color of the table.

myTable.whatIsMyColor = function() {
 console.log("My color is: " + this.color);



Adding a new property to an object

In JavaScript you can add a property to an object after it has been created.

The following statement adds the age property to the fighter object and assigns 22 to it:

fighter.age = 22;

Deleting a property of an object

Simply use the delete operator

delete fighter.age;

Checking if a property exists

To check if a property exists in an object, you use the in operator:

propertyName in objectName

The in operator returns true if the propertyName exists in the objectName.

The following example creates an employee object and uses the in operator to check if the ssn and employeeId properties exist in the object:

let employee = {
    firstName: 'Peter',
    lastName: 'Doe',
    employeeId: 1

console.log('ssn' in employee);
console.log('employeeId' in employee);Code language: JavaScript (javascript)




Javascript Arrays for Beginners (2023)

Arrays hold values.

An array is an ordered list of values.

Arrays are 0-based, in that the first value is 0, not 1 in terms of its position.

A JavaScript array has the following characteristics:

  1. First, an array can hold values of mixed types. For example, you can have an array that stores elements with the types number, string, boolean, and null.
  2. Second, the size of an array is dynamic and auto-growing. In other words, you don’t need to specify the array size up front.


W3schools describes an array as a “special variable, which can hold more than one value”.

An array can hold many values under a single name, and you can access the values by referring to an index number.

arrays w3schools


Creating & Fetching JavaScript arrays

JavaScript provides you with two ways to create an array. 

It is a common practice to declare arrays with the const keyword.

Image source

You can also use the following code to create a new array:

let values = new Array();


let values = [item1,item2,...]

Once you’ve created your array, you can print the values to the console.log with the code:


With “values” being the name of the array.

You can call “values.length” to get the length of the array


Again, in the above code “values” is the name of the array.

You can define and name an array, and then “push” values into it later:

The above code will add a single value of 5 to the array named “values”.

console.log(values[1]); will print the second value – 7

console.log(values[0]); will print the first value – 5

In summary – to create an array, it’s generally best to use the “const” keyword, or the “new” keyword.

Adding & Changing Stuff Within Arrays

Below, the array name is used,and the variable number to update, the first variable.

You can try it yourself on the w3 schools website.

Accessing Arrays

You access an array element by referring to the index number:

accessing arrays

You can also loop through arrays

Javascript Functions for Beginners

A function is a piece of code, that can be reused.

It’s similar to a variable but doesn’t hold a value like a variable does. So it’s not that much like a variable, but kind of is.

Screenshots are from the brilliant Javascript Course on Udemy here

The code on lines 16 and 17 shown in the image above, creates the function. It is named “logger”.

the shorter code logger(); is used to/for “invoke”, “running”, or “calling” the function.

Function Declerations Vs Expressions

Function Declerations

When you create a function with a name, then it is a function decleration.

Function statements, declare a function. A declared function can be used later when it is “invoked” or “called”.

Function declerations must start with “function”.

For example:

function mma() {

return 8;


The functioned mma is declared. to invoke it use the code mma();

You can call function declerations, above the code that creates it.

Function Expressions (good article here)

A JavaScript function can also be defined using an expression.

A function expression can be stored in a variable:

Image source

Function expressions are invoked to avoid polluting the global scope. Instead of your program being aware of many different functions, when you keep them anonymous, they are used and forgotten immediately.

To summarize, function declarations are utilized when you desire to establish a function in the global scope that can be accessed anywhere in your code. On the other hand, function expressions are employed to confine the accessibility of the function, reduce the weight of the global scope, and maintain a neat syntax.

JavaScript Arrow Function

Arrow functions have shorter syntax

They are best suited to non-method functions


Functions Calling Other Functions

An example, might be a function that cuts up fruit pieces, and then sends the result to a function that blends it into a smoothie.

The start function used above, will print out “I am first bo! 222222!!!”

Functions Summary

A function is like a procedure. It has tasks and calculates a value.

A function requires input and must return an output.

Functions need to be defined with the word “function” and brackets ()

Brackets can also be called paranthesies, and the input is sometimes called “arguments” or “parameters”.

Image source

Image Source

Javascript Fundamentals for Beginners [2023]

Notes taken from The Complete JavaScript Course 2023 on Udemy and from across the web.

Variables in Javascript

Variables are used to store values.

Variables can be thought of like a box in the ‘real world’.

A box can hold items and can be labelled so we know what is in it.

If we create a variable and label it “firstName”

let firstName = "Jonas"

Now if we “call” or publish “firstName” we will get a value of “Jonas”

This can be extremely useful. For example, if you were to use “firstName” in hundreds of places on a website, you can just change the variable value, and in theory, all the ‘firstNames’ will update with one change in the code.

Naming Conventions for Variables

Camel case

Camel case involves having no spaces between words and leaving the first letter lowercase.

for example – firstNamePerson is written in camel case.

I guess the capital letter looks a bit like a camel’s hump.

This isn’t a hard rule, but general practice.

Hard rules for Variable Names

Variable names can’t start with a number – e.g. 3years = 3; – would result in an error because of the number “3” in the name

Symbols are generally a bad idea in variable names. You can only use letters, numbers, underscores or dollar sign.

You can’t use reserved JS keywords. e.g. “new” is a reserved keyword, as is “function” and “name”.

Don’t use all uppercase letters for variable name either. Unless it is a “constant” that never changes, such as the value of PI


You declare variables with “let”, you can update the variable later, without using “let”.

Constant – used to declare variables that don’t change e.g. date of birth

Strings and Template Literals

Good tutorial here.

Template literals make it easier to build strings.

Template Literals allow you to create:

  • Multiline strings – strings (text) that spans several lines
  • String Formatting – you can change part of the string for values of variables – This is called “String Interpolation”
  • HTML Escaping – making it okay to include in HTML of a webpage

let str = `Template literal here`;

Multiline strings

In older versions of Javascript, to create a new line, or a multi-line string, you had to include the newline code


The template literals allow you to define multiline strings more easily because you need to add a new line in the string wherever you want:

let p =
`This text
span multiple lines`;

Type Conversion and Coercion

Type coercion, type conversion, typecasting, and type juggling: all different names that refer to the process of converting one data type into another. This process is present in almost every programming language and is an important concept in computer science.


What is Type Conversion?

Type conversion can be :

implicit – done automatically by the code already in place

explicit – done more manually by the developer

What is Type Coercion?

Explicit coercion happens when we want to coerce the value type to a specific type. Most of the time, explicit coercion in JavaScript happens using built-in functions such as String()Number(), and Boolean().

When we try to create operations in JavaScript using different value types, JavaScript coerces the value types for us implicitly.

This is one of the reasons why developers tend to avoid implicit coercion in JavaScript. Most of the time we get unexpected results from the operation if we don’t know exactly how JavaScript coerces the value types.

When coercion is done automatically, it can cause some weird outcomes and issues

image source

Truthy and Falsy Values in Javascript (Boolean thing)

Values are considered either truthy (evaluate to true) or falsy (evaluate to false) depending on how they are evaluated in a Boolean context.

In JS there are 6 incidences that result in, or are considered “Falsyies”

  • The primitive value undefined
  • The primitive value null
  • The empty string (''"")
  • The global property NaN
  • A number or BigInt representing 0 (0-00.0-0.00n)
  • The keyword false

All other values are considered “truthys”

When a value is truthy in Javascript, it does not means that the value is equal to true but it means that the value coerces to true when evaluated in a boolean context.

truthyOrFalsy(undefined); // Falsy Value 
truthyOrFalsy(NaN);       // Falsy Value
truthyOrFalsy(null)       // Falsy Value
truthyOrFalsy("");        // Falsy Value
truthyOrFalsy(false)      // Falsy Value
truthyOrFalsy(0);         // Falsy Value
truthyOrFalsy(-0);        // Falsy Value
truthyOrFalsy(0n);        // Falsy Value

Equality Operators == and ===

JavaScript ‘==’ operator: In Javascript, the ‘==’ operator is also known as the loose equality operator which is mainly used to compare two values on both sides and then return true or false. This operator checks equality only after converting both the values to a common type i.e type coercion.

The operator using “two equals signs”, “==” is a “loose equality operator”. It will try and convert (using “coercion”) the values and then compare them.

JavaScript ‘==’ operator: In Javascript, the ‘==’ operator is also known as the loose equality operator which is mainly used to compare two values on both sides and then return true or false. This operator checks equality only after converting both the values to a common type i.e type coercion.


Genearlly, or loosely speaking, “==” just checks the values.

The ‘===’ operator, is the “strict operator” and checks the value and the data-type are the same.

JavaScript ‘===’ operator: Also known as strict equality operator, it compares both the value and the type which is why the name “strict equality”.

Boolean Logic

Boolean Logic is a form of algebra that is centered around three simple words known as Boolean Operators: “Or,” “And,” and “Not.” These Boolean operators are the logical conjunctions between your keywords in a search to help broaden or narrow its scope.


Boolean logic dictates that all values are either true or false.

Boolean data is a type of “Primitive Data Types” in Javascript. You can think of boolean values, a bit like a switch that turns on or off.

Boolean uses operators such as “AND” and “OR”.

For the result to be true in the example shown above, both A and B in the example, need to be true.

With the “OR” operator, we just need A or B to be true, for the result to be “TRUE”.

NOT operators invert the logical operators.

Returns false if its single operand can be converted to true; otherwise, returns true.


Logical Operators

Image source

The Switch Statement

A quick, or easier way of doing a complicated “if else” statement.

Screenshots from Udemy Course – The Complete JavaScript Course 2023: From Zero to Expert!

The switch statement can be used so that you can perform different actions, when one of a range of conditions is met.

If the condition – e.g. “Monday” in the screenshot above, is met, then the code associated with Monday, will be executed.

If there is no match at all, then the default code, shown at the bottom left of the screenshot above, will be executed.

You can also use the if/else statement as an alternative to the switch statement

If Else alternative to Switch Statement

Statements & Expressions

An expression is a piece of code that produces a value. e.g. 3 + 4 is an expression, because it creates a value.

Numbers themselves are expressions.

Booleans, which produce “true or false” is an expression

A statement, does not produce a value.

The Conditional (Ternary) Operator

The conditional operator, allows us to write something similar to an “If Else Statement”, but all in one line.

Use a question mark ? after the condition is declared, and that write the code we want executed if condition is true.

The “else” block, or the equivalent of an else block, goes after a colon :

Strict Mode in Javascript

To activate “strict mode”, right at the top of your script, you have to type:

"use strict";

As you would expect,

"use strict"; Defines that JavaScript code should be executed in “strict mode”.

Strict mode, helps developers identify mistakes and bugs in the code.

Strict mode doesn’t allow you to do certain (incorrect) things and in other instances, it will visibly show you that you’ve created an error.

For example, if you spell a variable incorrectly,