What is JavaScript?

JavaScript is a dynamic language. JavaScript is used to add actions to the elements in your websites. In this blog, you are going to learn about JavaScript. At the end, you have good knowledge of JavaScript and why it is important in making websites.

Table of Contents:

• What is JavaScript?
• Why JavaScript is Important
• Basic Concepts of JavaScript
  • 1. Variables and Data Types
  • 2. Operators
  • 3. Functions
  • 4. Objects and Arrays
  • 5. Conditionals and Loops
• JavaScript Syntax
  • 1. Writing JavaScript Code
  • 2. Common Syntax Errors
  • 3. Comments
• How JavaScript Works in the Browser?
  • 1. The JavaScript Engine
  • 2. Document Object Model
  • 3. Event Handling and Listeners
• Key Features of JavaScript
• Applications of JavaScript
• Limitations of JavaScript
• JavaScript Versions
• Conclusion

What is JavaScript?

JavaScript is a flexible language that will help you create webpages. It will help the developers create buttons that perform actions, pop-up messages, and change content dynamically without reloading the page.

Brief History of JavaScript

JavaScript was created in 1995 by Brendan Eich while working at Netscape. Firstly, it was called Mocha, then LiveScript, and was finally called JavaScript. In 1997, it became standardized and was officially called ECMAScript. Now, JavaScript is one of the powerful languages that is used to build websites and apps. And today it is used by developers all over the world.

Why JavaScript is Important

JavaScript is very popular among developers. Let’s understand the reason why it is considered important among developers:

• Actionable: It allows you to add dynamic elements to your website without reloading the full content.
• Real-Time Updates: JavaScript is important to create a website that can update its content of the website without reloading the webpage. This is helpful in making websites where content changes dynamically.
• Making Web Apps: JavaScript helps you to create Popular web apps like  Gmail, Facebook, and other websites.
• Works Everywhere: JavaScript is used by most developers because it works on all browsers and devices.
• Helpful libraries: You can create websites easily with various JavaScript libraries like React and Vue.js

Basic Concepts of JavaScript

JavaScript is a universal programming language with several foundational components. Below are the concepts which is required to be understood by each beginner:

1. Variables and Data Types

Variables are used as storage containers for storing values. And this is used whenever it is required.

Example:

let name = "Intellipaat";

Data Types: It is used to specify the data type that a variable can store. Common data types include:

• String: “Hello”
• Number: 42, 3.14
• Boolean: true or  false
• Object: {name: “Intellipaat”, age: 15}
• Array: [1, 2, 3]

2. Operators

Operators are symbols used to perform operations on variables or values. Some common types of operators include:

Arithmetic Operators: It is used to perform mathematical calculations.

Example: +, -, *, /

let sum = 5 + 3; (Result: 8)

Comparison Operators: It is used to compare two values.

Example: ==, !=, >, <

5 > 3 (Result: true)

Logical Operators: It is used to combine multiple conditions.

Example: && (AND), || (OR), ! (NOT)

3. Functions

A function in JavaScript is defined as a block of code that can be used to perform a particular task in code. Once a function is created, it can be used multiple times in code.

Example:

function greet(name) {

  console.log("Hello, " + name);

}

greet("Intellipaat");

Output:

• Functions in JavaScript will help you in organizing code and avoiding repetition. You can pass the values as parameters inside the function and get some results as output.

4. Objects and Arrays

Objects are used to store collections of data in key-value pairs.

Example:

let person = {

  name: "Intellipaat",

  age: 25,

  isStudent: false

};

console.log(person);

Output:

Example: Storing multiple values inside a single variable

let numbers = [1, 2, 3, 4, 5];

5. Conditionals and Loops

Conditional statements in JavaScript allow you to run a particular block of code when certain conditions evaluate as true. You can use if-else statements to use conditionals inside code.

Example:

let age = 20;

if (age >= 18) {

  console.log("You are an adult.");

} else {

  console.log("You are a minor.");

}

Output:

Loops: In JavaScript, loops are used to repeat certain lines of code multiple times until a certain condition is met.

Example of a for loop:

for (let i = 0; i < 5; i++) {

  console.log(i);

}

Output:

JavaScript Syntax

JavaScript Syntax refers to the set of rules that are used to define how you can write code in JavaScript. Understanding these rules helps you a lot to run code correctly. Here are some of the syntax rules that everyone needs to follow while writing code:

1. Writing JavaScript Code

You can write JavaScript code either in an HTML file directly using the <script> tag, or by creating a new file with a .js extension. Here’s how you can do it:

In an HTML file:

<html>
  <head>
    <title>My JavaScript Page</title>
  </head>
  <body>
    <script>
      let message = "Hello, Intellipaat!";
      console.log(message);
    </script>
  </body>
</html>

In an external .js file:

For linking the external script.js file to your HTML, use the <script> tag with the src attribute:

<script src="script.js"></script>

2. Common Syntax Errors

Here are some of the common errors that you may find while writing and running code in JavaScript:

Missing semicolon: Every line of code should end with a semicolon (;).

Incorrect:

let name = "Intellipaat"

console.log(name)

Correct:

let name = "Intellipaat";

console.log(name);

Unmatched parentheses or curly braces: Always make sure you close parentheses () and curly braces {}.

Incorrect:

if (x > 10 {

  console.log("Greater than 10");

Correct:

if (x > 10) {

  console.log("Greater than 10");

}

Using reserved keywords: Some words are reserved by JavaScript and cannot be used as variable names (like let, function, etc.).

Incorrect:

let function = "Hello, Intellipaat";

Correct:

let greeting = "Hello, Intellipaat";

3. Comments

Comments in JavaScript play a very important role when you are working in a team. It will help others to understand the code. In JavaScript, there are two types of comments in JavaScript:

Single-line comment: Starts with //, and everything after that on the same line is ignored by JavaScript.

Example:

// This is a single-line comment

let name = "Intellipaat";  // This is an inline comment

Multi-line comment: Starts with /* and ends with */. It’s used for commenting multiple lines of code.

Example:

/* This is a 

   multi-line comment */

let age = 25;

Documentation comments: It is used to explain the function or code blocks. Documentation comments are always written in multiple lines.

Example:

/**

 * This function calculates the area of a rectangle.

 * @param {number} width - The width of the rectangle.

 * @param {number} height - The height of the rectangle.

 * @returns {number} The area of the rectangle.

 */

function calculateArea(width, height) {

  return width * height;

}

How JavaScript Works in the Browser?

JavaScript is a dynamic language that will help you to do things like modify the text or update a page without reloading the page. Here is complete information about the working of JavaScript:

1. The JavaScript Engine

Every browser has a JavaScript engine that is responsible for running the JavaScript code inside the console. When you are opening a website on the browser, the browser loads the JavaScript and first checks for mistakes. Then it runs the code.

Every web browser uses a different JavaScript engine:

• Google Chrome uses the V8 engine.
• Firefox uses the SpiderMonkey engine.
• Safari uses the JavaScriptCore engine.

2. Document Object Model

The DOM is the blueprint for the webpage, it contains headings, buttons, and other HTML elements in a tree-like structure.JavaScript uses the DOM to change things on the page without needing to reload the full page.

For example, JavaScript can:

• You can change the text on a button.
• You can add new elements, like images or paragraphs.
• You can also change the style, like changing a button to red when clicked.

Example: The text of the button changed when the user clicked.

<button id="myButton">Click Me</button>
<script>
  const button = document.getElementById("myButton");
  button.addEventListener("click", function() {
    button.innerHTML = "You Clicked Me!";
  });
</script>

Here,

• When you click the button, JavaScript changes its text using the DOM.

3. Event Handling and Listeners

Whenever any user can take actions, like clicking on a button, typing, or scrolling the page, then it will be marked as events in JavaScript, and events are handled using event listeners in JavaScript. 

For example, JavaScript can listen for a click on a button and show a message:

<button id="myButton">Click Me</button>

<script>

  const button = document.getElementById("myButton");

  button.addEventListener("click", function() {

    alert("Button clicked!");

  });

</script>

Here,

• When the button is clicked, JavaScript shows an alert saying “Button clicked!” because it is listening for the click event.

Key Features of JavaScript

JavaScript is very popular among developers. Here are some of the features of JavaScript:

• Frameworks like React and Vue.js are used to write client-side code.
• You can perform an action when a user clicks on the button or performs an action.
• In JavaScript, there is no need to define the type of the variable. It can be automatically assigned at runtime.
• JavaScript allows running multiple operations at the same time.
• JavaScript is object oriented language, which means you can create and store data in the form of objects.
• JavaScript is built to run on all browsers and devices.
• JavaScript offers various libraries and frameworks for writing frontend and backend code.

Applications of JavaScript

Here are some of the common applications of JavaScript:

• JavaScript is used to create elements like buttons, forms, and animations on websites through which users can interact.
• Web Development Frameworks: JavaScript provides frameworks like React, Angular, and Vue to build web applications.
• Server-Side Development: JavaScript provides you 
• Mobile Apps: JavaScript is used to develop cross-platform mobile apps with frameworks like React Native.
• Game Development: JavaScript can be used to create simple browser-based games using HTML5 canvas.
• Browser Extensions: JavaScript is used to build browser extensions that add features to web browsers like Chrome and Firefox.
• Web APIs: JavaScript interacts with Web APIs to fetch data (e.g., weather info or social media feeds) and update the web page in real time.
• Real-Time Applications: JavaScript helps build real-time applications like chat apps and live notifications.

Limitations of JavaScript

JavaScript is great, but it does have some limitations. Let’s see what those limitations are:

• Works Only in Browsers: JavaScript mostly works in web browsers, so it’s not as useful outside of websites, though it can run on servers with Node.js.
• Security Issues: JavaScript can be vulnerable to attacks if not properly protected, like code injections (XSS).
• Can Be Slow: For complex tasks, JavaScript may be slower compared to other programming languages.
• Single Inheritance: JavaScript allows only one parent object for each object, unlike other languages that can have multiple parent objects.
• Different Browsers, Different Results: JavaScript might behave differently in different browsers, causing issues for developers.
• No Multithreading: JavaScript runs on one thread, so it can struggle with tasks that need to happen at the same time, though there are solutions like Web Workers.
• Depends on the Browser: JavaScript performance can vary depending on the browser, so what works well in one may not in another.

JavaScript Versions

Conclusion

Till now, you learn a lot about JavaScript and its importance in the web development field. JavaScript helps you to create websites easily, and not only websites, but it is also helpful in creating applications. And it is used by most of the developers around the world.

What is JavaScript – FAQs