Front End Web Development - Complete Course With Examples - Part 2

 Front End Web Development - Complete Course Part 2

•  Introduction to JavaScript

JavaScript is a programming language that is commonly used to add interactive features to websites. It is an essential part of front-end web development, and it is supported by all modern web browsers.

JavaScript is a dynamic and loosely-typed language that is used to manipulate HTML and CSS, create animations, and handle user input. It is often used to validate forms, create cookies, and make asynchronous requests to servers.

JavaScript code is usually written in separate files and included in an HTML document using a <script> element. It can also be included directly in an HTML document within a <script> element.

Here is an example of a simple JavaScript script that displays an alert message:

 JavaScript is a powerful and versatile language that has a large and active community of developers. It is constantly evolving and has a wide range of libraries and frameworks that can be used to build complex and interactive web applications.

• Basic syntax and data types

JavaScript has a C-style syntax, which means that it uses curly braces to denote blocks of code and semicolons to separate statements.

Here is an example of a simple JavaScript function that takes a message as an argument and displays it in an alert box:

 

In this example, the showMessage function is defined with a single parameter, message. The function uses the alert function to display the value of the message parameter in an alert box. The function is then called with the string "Hello, world!" as an argument.

JavaScript has a number of data types, including:

• Numbers: JavaScript has a single numeric data type, which can represent both integers and floating-point numbers.

• Strings: JavaScript strings are used to represent text and are denoted by either single or double quotes.

• Booleans: JavaScript has a boolean data type that can represent the values true and false.

• Arrays: JavaScript arrays are used to store ordered collections of values. They are denoted by square brackets and can contain any data type.

• Objects: JavaScript objects are used to store collections of key-value pairs. They are denoted by curly braces and can contain any data type.

  Here is an example of using different data types in JavaScript:
  

 In this example, the num variable is assigned the value 42 (a number), the str variable is assigned the value "hello" (a string), the bool variable is assigned the value true (a boolean), the arr variable is assigned an array of numbers, and the `obj

• Control structures and functions
  
  JavaScript has a number of control structures that allow you to control the flow of your code, including:

  if statements: if statements are used to execute a block of code if a condition is true.

  for loops: for loops are used to repeat a block of code a certain number of times.

  while loops: while loops are used to repeat a block of code as long as a condition is true.

  Here is an example of using an if statement and a for loop in JavaScript:

 

In this example, the if statement checks if the value of the num variable is even or odd, and the for loop iterates from 0 to 4 and logs the current value of i to the console on each iteration.

JavaScript also has functions, which are blocks of code that can be reused and invoked multiple times. Functions can take arguments and return a value.

Here is an example of defining and calling a function in JavaScript:

•  Working with the Document Object Model (DOM)

The Document Object Model (DOM) is a programming interface for HTML and XML documents. It represents the structure of a document as a tree-like hierarchy of objects, and it allows you to modify the content, style, and event behavior of a webpage.

Using the DOM, you can access and manipulate elements in an HTML or XML document using JavaScript. You can use DOM methods to create new elements, delete elements, change their content and attributes, and respond to events.

Here is an example of using the DOM to change the text of an element:

 In this example, the getElementById method is used to get a reference to the element with an ID of "main-heading". The innerHTML property is then used to set the content of the element to the string "Hello, world!".

You can also use DOM methods to add event listeners to elements, which allow you to execute code in response to specific events, such as clicks, hover events, and form submissions.

Here is an example of using the DOM to add a click event listener to a button:

 

In this example, the addEventListener method is used to add a click event listener to the button element. The anonymous function passed as an argument is executed whenever the button is clicked.

The DOM is an essential part of front-end web development, and it is an important aspect of working with JavaScript. By using the DOM, you can create dynamic and interactive web applications that respond to user input and events.

Responsive design and mobile development

• Introduction to responsive design

Responsive design is the practice of designing websites that adapt to the size and orientation of the user's device. This allows a website to be easily viewed on different devices, such as desktop computers, tablets, and smartphones.

Responsive design is achieved using media queries, which allow you to apply different styles based on the width of the viewport. Viewport width is a measure of the width of the browser window, and it is used to determine the size of the device.

Here is an example of using media queries to create a responsive layout: