QP School - JavaScript Tutorials

Everything you need to know about JavaScript

Tue, 25 Jul 2023 11:51:28 +0200

JavaScript is a high-level, dynamic, and versatile programming language primarily used for web development. It was created by Brendan Eich while he was working at Netscape and first appeared in 1995. Since then, it has become one of the most widely used programming languages, not only for web development but also for server-side development (Node.js), desktop applications, game development, and more. Here's everything you need to know about JavaScript:

Client-Side Scripting: JavaScript is primarily used as a client-side scripting language, meaning it runs on the user's web browser and allows developers to create interactive and dynamic web pages. It can manipulate HTML and CSS, handle user interactions, and respond to events like button clicks and form submissions.

Syntax and Structure: JavaScript syntax is similar to other programming languages like C, Java, and C++, making it relatively easy for developers with programming experience to learn. It uses variables, functions, loops, conditionals, and other familiar programming constructs.

Data Types: JavaScript is a dynamically-typed language, meaning you don't need to declare the data type of a variable explicitly. Common data types include numbers, strings, booleans, objects, arrays, and functions.

Objects and Prototypes: JavaScript is an object-oriented language, and everything in JavaScript is an object, except for primitive data types. It uses prototype-based inheritance, where objects can inherit properties and methods from other objects.

Functions: Functions are a core concept in JavaScript. They can be defined using the function keyword and can be assigned to variables, passed as arguments to other functions, and returned from functions.

Event Handling: JavaScript is widely used for event handling in web development. Events like clicks, keypresses, and form submissions can be captured, and corresponding functions can be executed in response.

Asynchronous Programming: JavaScript supports asynchronous programming through callbacks, promises, and async/await. Asynchronous functions allow non-blocking execution, making it suitable for tasks like fetching data from servers without freezing the user interface.

DOM Manipulation: The Document Object Model (DOM) is a programming interface for HTML and XML documents. JavaScript allows developers to access, modify, and manipulate the DOM, enabling dynamic changes to web pages after they have loaded.

Libraries and Frameworks: JavaScript has a rich ecosystem of libraries and frameworks that simplify and expedite web development. Some popular ones include jQuery, React, Angular, Vue.js, and Express.js (for server-side development).

Cross-Browser Compatibility: JavaScript code runs on various web browsers, but browser implementations may vary. Developers need to consider cross-browser compatibility and test their code on different browsers.

Security Considerations: Since JavaScript executes on the client-side, security is a crucial aspect. Developers must be mindful of potential security vulnerabilities like Cross-Site Scripting (XSS) and Cross-Site Request Forgery (CSRF) and implement security measures to protect users and their data.

ES6 and Beyond: ECMAScript 6 (ES6) is a major update to the JavaScript language, introducing new syntax, features, and enhancements. Many modern JavaScript projects use ES6 or later versions, taking advantage of features like arrow functions, classes, modules, and more.

JavaScript's versatility and wide adoption have made it an essential skill for web developers. As the language continues to evolve, it remains a fundamental tool for building interactive and responsive web applications.

JavaScript - Array find() example (returns the value)

Tue, 04 Apr 2023 10:12:03 +0200

The HTML part between the tags looks like this:

Code:

Click "Test" to return the value of the first element in the array that has a value above this number:

The JavaScript part looks like this:

Code:
const ages = [4, 12, 16, 20];

function checkAge(age)

{

  return age > document.getElementById("ageToCheck").value;

}

function myFunction()

{

  document.getElementById("demo").innerHTML = ages.find(checkAge);

}

JavaScript Array findIndex() examples (returns the index)

Tue, 04 Apr 2023 10:10:16 +0200

The HTML part between the tags looks like this:

Code:

Example 1




Example 2


Click "Test" to return the index of the first array element that has a value above this number:

The JavaScript part looks like this:

Code:
// Example 1

const ages = [3, 10, 18, 20];

function checkAge(age)

{

  return age > 18;

}

document.getElementById("demo").innerHTML = ages.findIndex(checkAge);

// Example 2

const numbers = [4, 12, 16, 20];

function checkValue(x)

{

  return x > document.getElementById("toCheck").value;

}

function myFunction()

{

  document.getElementById("demo2").innerHTML = numbers.findIndex(checkValue);

}

JavaScript - Additions with values

Tue, 04 Apr 2023 10:05:34 +0200

Code:
let x = 100 + 50;

document.getElementById("demo").innerHTML = x;

JavaScript - Additions with variables

Tue, 04 Apr 2023 10:05:07 +0200

Code:
let a = 100;

let b = 50;

let x = a + b;

document.getElementById("demo").innerHTML = x;

JavaScript - Additions with expressions

Tue, 04 Apr 2023 10:04:40 +0200

Code:
let a = 3;

let x = (100 + 50) + a;

document.getElementById("demo").innerHTML = x;

JavaScript - Subtractions with values

Tue, 04 Apr 2023 10:04:09 +0200

Code:
let a = 10 - 5;

document.getElementById("demo").innerHTML = a;

JavaScript - Subtractions with variables

Tue, 04 Apr 2023 10:03:37 +0200

Code:
let a = 10;

let b = 5;

let c = a - b;

document.getElementById("demo").innerHTML = c;

JavaScript - Subtractions with expressions

Tue, 04 Apr 2023 10:02:29 +0200

Code:
let a = 1;

let b = (10 - 1) - a;

document.getElementById("demo").innerHTML = b;

JavaScript - Multiplications with values

Tue, 04 Apr 2023 10:02:01 +0200

Code:
let a = 2 * 2;

document.getElementById("demo").innerHTML = a;

JavaScript - Multiplications with variables

Tue, 04 Apr 2023 10:01:34 +0200

Code:
let a = 2;

let b = 2;

let c = a * b;

document.getElementById("demo").innerHTML = c;

JavaScript - Multiplications with expressions

Tue, 04 Apr 2023 10:01:06 +0200

Code:
let a = 2;

let b = (2 * 2) * 2;

document.getElementById("demo").innerHTML = b;

JavaScript - Divisions with values

Tue, 04 Apr 2023 10:00:37 +0200

Code:
let a = 4 / 2;

document.getElementById("demo").innerHTML = a;

JavaScript - Divisions with variables

Tue, 04 Apr 2023 10:00:11 +0200

let a = 4;
let b = 2;
let c = a / b;

document.getElementById("demo").innerHTML = c;

JavaScript - Divisions with expressions

Tue, 04 Apr 2023 09:59:45 +0200

Code:
let a = 8;

let b = (8 / 2) / 2;

document.getElementById("demo").innerHTML = b;