JavaScript Tutorial

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Tamim Ahmed

17 Mar 2023 (1 week ago)

Araihazar, Narayanganj, Dhaka, Bangladesh

JavaScript Tutorial

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Welcome to the JavaScript tutorial! JavaScript is a popular programming language that is used to create interactive websites, dynamic web applications, and server-side scripts. In this tutorial, we will cover the basics of JavaScript and provide you with the knowledge to start building your own web applications.

What is JavaScript?

JavaScript is a programming language that was created to add interactivity to web pages. It is a high-level, interpreted language that is used to create dynamic and interactive web pages. It is a client-side language, which means that it runs on the client-side (i.e. the web browser) and not on the server-side.

Getting started with JavaScript

To start using JavaScript, you need to have a text editor to write your code, and a web browser to run your code. You can use any text editor that you like, such as Sublime Text, Atom, Visual Studio Code, or Notepad++.

To create a JavaScript file, create a new file in your text editor and save it with the “.js” extension. For example, you could save it as “myscript.js”.

Once you have created your JavaScript file, you can link it to your HTML file using the <script> tag. Here’s an example:

<!DOCTYPE html>
<html>
<head>
  <title>My Website</title>
</head>
<body>
  <h1>Hello, world!</h1>
  <script src="myscript.js"></script>
</body>
</html>

In this example, the myscript.js file is linked to the HTML file using the <script> tag. The src attribute specifies the path to the JavaScript file.

Basic syntax

JavaScript syntax is similar to other programming languages such as Java and C++. Here’s an example of a simple JavaScript program:

// This is a comment
alert("Hello, world!"); // This displays an alert box with the message "Hello, world!"

In this example, we use the alert() function to display an alert box with the message “Hello, world!”. The double forward slashes (//) indicate a comment, which is ignored by the JavaScript interpreter.

Variables

Variables are used to store values in JavaScript. To create a variable, you use the var, let, or const keyword, followed by the name of the variable. Here’s an example:

var message = "Hello, world!";
let x = 5;
const PI = 3.14159;

In this example, we create three variables: message, x, and PI. The var keyword is used to create the message variable, the let keyword is used to create the x variable, and the const keyword is used to create the PI variable. The message variable is a string, the x variable is a number, and the PI variable is a constant.

Data types

JavaScript supports several data types, including numbers, strings, booleans, objects, and arrays. Here’s an example:

var age = 25; // a number
var name = "John"; // a string
var isMale = true; // a boolean
var person = { name: "John", age: 25 }; // an object
var fruits = ["apple", "banana", "orange"]; // an array

In this example, we create variables for each of the data types: a number (age), a string (name), a boolean (isMale), an object (person), and an array (fruits).

Why Study JavaScript?

There are several reasons why studying JavaScript is beneficial, particularly for those interested in web development:

Client-side web development: JavaScript is the primary language used for client-side web development, which means that it is responsible for the interactivity and dynamic behavior of web pages. By studying JavaScript, you can learn how to create interactive web pages and web applications.
Server-side web development: JavaScript can also be used for server-side web development, using platforms such as Node.js. This allows you to use the same language for both client-side and server-side development, providing greater consistency and flexibility.
High demand for JavaScript developers: JavaScript is one of the most popular programming languages in the world, and there is a high demand for skilled JavaScript developers. By studying JavaScript, you can increase your job prospects and earn a higher salary.
Career growth opportunities: Learning JavaScript can lead to opportunities for career growth and advancement in the field of web development. As you gain experience and expertise in JavaScript, you can move into more specialized roles such as full-stack developer, front-end developer, or back-end developer.
Wide range of frameworks and libraries: There are a wide range of JavaScript frameworks and libraries available, such as React, Angular, Vue.js, and jQuery. By studying JavaScript, you can learn how to use these tools to build more efficient and powerful web applications.

Overall, studying JavaScript can open up a world of possibilities in web development, providing you with the skills and knowledge needed to build dynamic, interactive, and engaging web applications.

JavaScript Introduction

JavaScript is a high-level, interpreted programming language used primarily to create interactive web pages and web applications. It was first developed by Brendan Eich at Netscape Communications in 1995, and since then has become one of the most popular programming languages in the world.

JavaScript is primarily used for client-side web development, which means that it is executed in the user’s web browser rather than on the server-side. This allows JavaScript to create dynamic and interactive web pages that respond to user input and events.

JavaScript is also used for server-side web development, using platforms such as Node.js. This allows developers to use the same language for both client-side and server-side development, providing greater consistency and flexibility.

JavaScript is a versatile language that can be used for a wide range of applications, from simple scripts to complex web applications. It supports a wide range of programming paradigms, including object-oriented programming, functional programming, and procedural programming.

JavaScript is also supported by a wide range of frameworks and libraries, such as React, Angular, Vue.js, and jQuery. These tools allow developers to build more efficient and powerful web applications with less code.

Overall, JavaScript is an essential tool for web developers, providing the ability to create dynamic and interactive web applications that engage users and provide a seamless user experience.

JavaScript Can Change HTML Content

Yes, JavaScript can change the HTML content of a web page dynamically, without requiring a full page reload. This is known as Dynamic HTML (DHTML), and it enables developers to create more interactive and responsive web pages.

JavaScript can manipulate HTML elements using the Document Object Model (DOM). The DOM is a programming interface for web documents that allows developers to access and manipulate the content and structure of HTML and XML documents.

Using JavaScript, developers can modify the content, attributes, and styles of HTML elements on a web page. For example, the following JavaScript code changes the text content of a paragraph element with the ID “demo”:

document.getElementById("demo").innerHTML = "Hello, world!";

This code uses the getElementById() method to select the paragraph element with the ID “demo”, and then sets its innerHTML property to the new text content.

In addition to modifying text content, JavaScript can also manipulate other HTML attributes and styles. For example, the following code changes the background color of a button element when it is clicked:

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

button.onclick = function() {
  button.style.backgroundColor = "red";
};

This code assigns a click event handler to the button element with the ID “myButton”. When the button is clicked, the event handler function changes the button’s backgroundColor style property to “red”, causing the button to change color.

Overall, JavaScript’s ability to dynamically modify HTML content and styles allows developers to create more engaging and interactive web pages that respond to user actions and events.

JavaScript Can Change HTML Attribute Values

Yes, JavaScript can change the values of HTML attributes dynamically. The Document Object Model (DOM) provides several methods and properties that enable developers to access and modify HTML attributes.

To change the value of an attribute using JavaScript, you can use the setAttribute() method. This method takes two arguments: the name of the attribute to set, and the new value of the attribute. For example, the following JavaScript code changes the src attribute of an img element:

var myImg = document.getElementById("myImg");
myImg.setAttribute("src", "new_image.jpg");

This code selects the img element with the ID “myImg” using the getElementById() method, and then sets its src attribute to “new_image.jpg” using the setAttribute() method.

Similarly, you can use the getAttribute() method to retrieve the value of an attribute, and the removeAttribute() method to remove an attribute from an element. For example:

var myLink = document.getElementById("myLink");

// Get the value of the href attribute
var hrefValue = myLink.getAttribute("href");

// Remove the target attribute
myLink.removeAttribute("target");

In this code, the first line selects the a element with the ID “myLink”. The getAttribute() method is then used to retrieve the value of the href attribute, which is stored in the hrefValue variable. Finally, the removeAttribute() method is used to remove the target attribute from the a element.

Overall, JavaScript provides a powerful set of tools for manipulating HTML attributes dynamically, enabling developers to create more dynamic and interactive web pages.

JavaScript Can Change HTML Styles (CSS)

Yes, JavaScript can change HTML styles (CSS) dynamically, allowing developers to modify the appearance of HTML elements on a web page in response to user actions or other events.

To change the style of an HTML element using JavaScript, you can use the style property of the element. The style property is an object that represents the inline styles of the element, and provides properties for each style attribute.

For example, the following JavaScript code changes the background color of a div element with the ID “myDiv”:

var myDiv = document.getElementById("myDiv");
myDiv.style.backgroundColor = "blue";

This code selects the div element with the ID “myDiv” using the getElementById() method, and then sets its backgroundColor style property to “blue” using the style property.

In addition to setting individual style properties, you can also set multiple styles at once using the cssText property. For example:

var myDiv = document.getElementById("myDiv");
myDiv.style.cssText = "background-color: blue; color: white; font-size: 24px;";

This code sets the cssText property of the style object to a string containing multiple style declarations, separated by semicolons.

You can also use JavaScript to add, remove, or toggle CSS classes on an element using the classList property. For example, the following code adds a CSS class called “active” to a div element with the ID “myDiv”:

var myDiv = document.getElementById("myDiv");
myDiv.classList.add("active");

This code selects the div element with the ID “myDiv” using the getElementById() method, and then adds the “active” CSS class to its classList property using the add() method.

Overall, JavaScript provides a flexible and powerful set of tools for changing HTML styles (CSS) dynamically, allowing developers to create more engaging and interactive web pages.

JavaScript Can Hide HTML Elements

Yes, JavaScript can hide HTML elements dynamically using the style property of the element. There are several ways to hide an HTML element using JavaScript, including setting its display property to “none”, setting its visibility property to “hidden”, or changing its opacity property to 0.

For example, to hide a div element with the ID “myDiv” using the display property, you can use the following JavaScript code:

var myDiv = document.getElementById("myDiv");
myDiv.style.display = "none";

This code selects the div element with the ID “myDiv” using the getElementById() method, and then sets its display property to “none” using the style property. This will hide the element completely, and it will not take up any space on the web page.

To show the element again, you can set its display property back to its original value. For example:

var myDiv = document.getElementById("myDiv");
myDiv.style.display = "block"; // or "inline", "inline-block", etc.

This code sets the display property of the div element back to its original value, which could be “block”, “inline”, “inline-block”, or any other valid value for the display property.

Similarly, you can hide an element using the visibility property by setting it to “hidden”, or by changing its opacity property to 0. For example:

// Hide an element using the visibility property
var myDiv = document.getElementById("myDiv");
myDiv.style.visibility = "hidden";

// Hide an element using the opacity property
var myDiv = document.getElementById("myDiv");
myDiv.style.opacity = 0;

In both of these examples, the element will be hidden from view, but it will still take up space on the web page. To show the element again, you can set its visibility property back to “visible”, or its opacity property back to 1.

Overall, JavaScript provides several options for hiding HTML elements dynamically, allowing developers to create more interactive and responsive web pages.

JavaScript Where To

In web browsers: JavaScript is most commonly used in web browsers to add interactivity and dynamic behavior to web pages. JavaScript can be embedded directly in HTML files or included as a separate file.
Server-side: JavaScript can also be used on the server-side using frameworks such as Node.js. This allows developers to use the same language on both the front-end and back-end of web applications.
Mobile applications: JavaScript can be used in mobile applications using frameworks such as React Native or Ionic. These frameworks allow developers to build native mobile applications using web technologies, including JavaScript.
Desktop applications: JavaScript can also be used to build desktop applications using frameworks such as Electron. Electron allows developers to create cross-platform desktop applications using web technologies.
Internet of Things (IoT): JavaScript can also be used in IoT devices using platforms such as Johnny-Five or Tessel. These platforms provide a way to interact with hardware devices using JavaScript.

Overall, JavaScript is a versatile language that can be used in a variety of contexts, making it a popular choice for web developers and beyond.

The <script> Tag

The <script> tag is used to define a block of JavaScript code within an HTML document. The <script> tag can be placed in various locations within an HTML document, including the <head> section, the <body> section, or even within an HTML element.

Here is an example of how the <script> tag is used to include JavaScript code in an HTML document:

<!DOCTYPE html>
<html>
<head>
  <title>My Web Page</title>
  <script>
    // JavaScript code goes here
    alert("Hello, world!");
  </script>
</head>
<body>
  <h1>Welcome to my web page</h1>
  <p>This is some content.</p>
</body>
</html>

In this example, the <script> tag is placed in the <head> section of the HTML document, and contains a simple JavaScript code that displays an alert dialog with the message “Hello, world!”.

You can also use the src attribute of the <script> tag to include an external JavaScript file in your HTML document. For example:

<!DOCTYPE html>
<html>
<head>
  <title>My Web Page</title>
  <script src="my-script.js"></script>
</head>
<body>
  <h1>Welcome to my web page</h1>
  <p>This is some content.</p>
</body>
</html>

In this example, the src attribute is used to include an external JavaScript file called “my-script.js”. This file should contain the JavaScript code you want to run on your web page.

JavaScript in <head> or <body>

JavaScript code can be placed in both the <head> and <body> sections of an HTML document, but there are some differences between the two approaches.

Placing JavaScript code in the <head> section:

When you place JavaScript code in the <head> section, the code is executed before the web page is fully loaded. This means that if your JavaScript code manipulates the HTML elements on the web page, those elements may not exist yet when the code runs. This can cause errors or unexpected behavior.

However, placing JavaScript code in the <head> section can also have some advantages. For example, you can use it to load external JavaScript files or define global variables and functions that can be used throughout the web page. Here’s an example of how to include JavaScript code in the <head> section:

<!DOCTYPE html>
<html>
<head>
  <title>My Web Page</title>
  <script src="my-script.js"></script>
</head>
<body>
  <h1>Welcome to my web page</h1>
  <p>This is some content.</p>
</body>
</html>

Placing JavaScript code in the <body> section:

When you place JavaScript code in the <body> section, the code is executed after the web page has finished loading. This means that all of the HTML elements on the web page will exist when the code runs, which can help to prevent errors or unexpected behavior.

Here’s an example of how to include JavaScript code in the <body> section:

<!DOCTYPE html>
<html>
<head>
  <title>My Web Page</title>
</head>
<body>
  <h1>Welcome to my web page</h1>
  <p>This is some content.</p>
  <script>
    // JavaScript code goes here
    alert("Hello, world!");
  </script>
</body>
</html>

In this example, the JavaScript code is placed in the <body> section after the HTML elements. This ensures that the HTML elements will exist before the code runs.

Overall, the best approach depends on the specific requirements of your web page and the JavaScript code you want to run. In general, it’s a good idea to place JavaScript code in the <body> section, unless you have a specific reason to place it in the <head> section.

External JavaScript

External JavaScript is JavaScript code that is stored in a separate file, rather than being included directly in an HTML document. This can make your code easier to manage and maintain, especially if you have a lot of JavaScript code on your web page.

To use external JavaScript, you need to create a separate file that contains your JavaScript code, and then include that file in your HTML document using the <script> tag’s src attribute.

Here’s an example of how to create an external JavaScript file and include it in an HTML document:

Create a new file called “my-script.js” and save it in the same directory as your HTML file.
Add your JavaScript code to the “my-script.js” file. For example:

function showMessage() {
  alert("Hello, world!");
}

3. In your HTML file, add a <script> tag to include the “my-script.js” file. For example:

<!DOCTYPE html>
<html>
<head>
  <title>My Web Page</title>
  <script src="my-script.js"></script>
</head>
<body>
  <h1>Welcome to my web page</h1>
  <p>This is some content.</p>
  <button onclick="showMessage()">Click me!</button>
</body>
</html>

In this example, the <script> tag’s src attribute is set to “my-script.js”. This tells the browser to load the “my-script.js” file and execute its JavaScript code.

Once you have included the external JavaScript file in your HTML document, you can use any functions or variables defined in that file, just as you would with JavaScript code included directly in the HTML document.

JavaScript Output

JavaScript can output information to the user in several ways, including:

Using the alert() method: The alert() method displays a dialog box with a message and an “OK” button. For example:

alert("Hello, world!");

Using the console.log() method: The console.log() method outputs information to the console of the browser’s developer tools. This is useful for debugging and testing purposes. For example:

console.log("Hello, world!");

Using the document.write() method: The document.write() method writes text directly to the HTML document. However, this method is generally not recommended for production websites, as it can overwrite the entire HTML document if used improperly. For example:

document.write("Hello, world!");

Using the innerHTML property: The innerHTML property can be used to set the HTML content of an element on the web page. For example:

document.getElementById("my-element").innerHTML = "Hello, world!";

In this example, the innerHTML property sets the content of an HTML element with the ID “my-element” to “Hello, world!”.

Overall, the choice of which output method to use depends on your specific requirements and the context in which your JavaScript code is running. For example, if you want to display a simple message to the user, the alert() method might be appropriate. If you’re debugging your code, the console.log() method might be more useful. If you need to output complex HTML content, the innerHTML property might be the best choice.

Using innerHTML

The innerHTML property in JavaScript can be used to change the content of an HTML element on the web page. Here’s an example:

<!DOCTYPE html>
<html>
<head>
  <title>My Web Page</title>
</head>
<body>
  <h1 id="my-heading">Welcome to my web page</h1>
  <p id="my-paragraph">This is some content.</p>
  <script>
    // Change the content of the <h1> element
    document.getElementById("my-heading").innerHTML = "Hello, world!";
    
    // Change the content of the <p> element
    document.getElementById("my-paragraph").innerHTML = "This is some new content.";
  </script>
</body>
</html>

In this example, the innerHTML property is used to change the content of two HTML elements: the <h1> element with the ID “my-heading” and the <p> element with the ID “my-paragraph”. The JavaScript code uses the document.getElementById() method to select the elements and then sets their innerHTML property to the desired content.

Note that when you use innerHTML to change the content of an HTML element, you can include HTML tags and attributes in the new content. For example, you could set the content of a <div> element to an entire web page, including the <html>, <head>, and <body> tags.

However, be careful when using innerHTML to insert user-generated content into your web page, as this can expose your website to cross-site scripting (XSS) attacks. To prevent XSS attacks, you should always sanitize and validate user input before using it in your innerHTML statements.

JavaScript Statements

JavaScript code is made up of statements, which are the individual instructions that tell the computer what to do. A statement is typically terminated with a semicolon (;) and can span multiple lines.

Here are some common types of JavaScript statements:

Variable declaration: A variable is a container for a value. In JavaScript, you can declare a variable using the var, let, or const keywords, followed by the variable name and optionally an initial value. For example:

var myVariable = "Hello, world!";
let anotherVariable = 42;
const PI = 3.14;

Assignment: You can assign a value to a variable using the = operator. For example:

myVariable = "Goodbye, world!";

Arithmetic: You can perform arithmetic operations using operators such as +, -, *, /, and % (modulo). For example:

let sum = 5 + 3; // sum is now 8
let difference = 5 - 3; // difference is now 2
let product = 5 * 3; // product is now 15
let quotient = 5 / 3; // quotient is now approximately 1.67
let remainder = 5 % 3; // remainder is now 2

Conditional: You can use conditional statements, such as if, else if, and else, to execute different code depending on whether a condition is true or false. For example:

if (myVariable === "Hello, world!") {
  console.log("The variable is set to 'Hello, world!'");
} else {
  console.log("The variable is not set to 'Hello, world!'");
}

Loops: You can use loop statements, such as for and while, to execute code repeatedly. For example:

for (let i = 0; i < 5; i++) {
  console.log(i);
}

let j = 0;
while (j < 5) {
  console.log(j);
  j++;
}

Functions: You can define and call functions, which are reusable blocks of code that can accept parameters and return values. For example:

function square(number) {
  return number * number;
}

let result = square(5); // result is now 25

These are just a few examples of the many types of statements that are available in JavaScript. By combining these statements in various ways, you can create complex programs that perform a wide variety of tasks.

JavaScript Programs

A JavaScript program is a set of statements that are executed in a specific order to perform a task or achieve a goal. A program can be as simple as a single statement or as complex as a web application with thousands of lines of code.

Here’s an example of a simple JavaScript program that uses the alert() function to display a message in a popup window:

alert("Hello, world!");

This program consists of a single statement that calls the alert() function with the message “Hello, world!” as its argument. When the program is run, the alert() function displays a popup window with the message.

Here’s a more complex example of a JavaScript program that calculates the sum of two numbers and displays the result in the console:

let num1 = 5;
let num2 = 7;
let sum = num1 + num2;
console.log("The sum of " + num1 + " and " + num2 + " is " + sum + ".");

This program consists of four statements:

The first two statements declare and initialize two variables, num1 and num2, with the values 5 and 7, respectively.
The third statement calculates the sum of num1 and num2 and stores the result in the sum variable.
The fourth statement uses the console.log() function to display a message in the console that includes the values of num1, num2, and sum.

Here’s another example of a JavaScript program that prompts the user for their name, stores it in a variable, and displays a personalized greeting:

let name = prompt("What is your name?");
console.log("Hello, " + name + "!");

This program consists of two statements:

The first statement calls the prompt() function to display a dialog box that asks the user for their name and stores the result in the name variable.
The second statement uses the console.log() function to display a personalized greeting that includes the value of the name variable.

These examples demonstrate how JavaScript programs can perform a variety of tasks, from simple popup messages to complex calculations and interactions with the user. By combining the basic programming constructs, such as variables, operators, functions, and control structures, you can create powerful and flexible JavaScript programs that can run in a browser or on a server.

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Tamim Ahmed

17 Mar 2023 (1 week ago)

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What is JavaScript?

Getting started with JavaScript

Basic syntax

Variables

Data types

Why Study JavaScript?

JavaScript Introduction

JavaScript Can Change HTML Content

JavaScript Can Change HTML Attribute Values

JavaScript Can Change HTML Styles (CSS)

JavaScript Can Hide HTML Elements

JavaScript Where To

The <script> Tag

JavaScript in <head> or <body>

External JavaScript

JavaScript Output

Using innerHTML

JavaScript Statements

JavaScript Programs

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