javaScript is a programming language that is primarily used to add interactivity and dynamic behavior to web pages. It is a high-level, interpreted language that is designed to be easy to learn and use. Here's a complete guide to JavaScript that covers everything you need to know to get started with the language.

Getting Started

To start using JavaScript, you will need a basic understanding of HTML and CSS. JavaScript can be added to an HTML document using the <script> tag, either in the <head> or <body> section of the document. Here's an example of how to include a JavaScript file in an HTML document:

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<!DOCTYPE html>
<html>
  <head>
    <script src="script.js"></script>
  </head>
  <body>
    <h1>Hello World!</h1>
  </body>
</html>

In this example, the JavaScript code is stored in a separate file called script.js, which is included in the HTML document using the src attribute of the <script> tag.

Variables

Variables are used to store values in JavaScript. You can declare a variable using the var, let, or const keywords. Here's an example of how to declare a variable:

csharp
var message = "Hello World!";

In this example, the variable message is declared and assigned the value "Hello World!".

Data Types

JavaScript supports several data types, including strings, numbers, booleans, and objects. Here's an example of how to create a string variable:

csharp
var message = "Hello World!";

In this example, the string "Hello World!" is stored in the message variable.

Operators

JavaScript supports several types of operators, including arithmetic, assignment, comparison, and logical operators, three dots operator. Here's an example of how to use arithmetic operators:

csharp
var x = 10;
var y = 5;
var z = x + y;

In this example, the variables x and y are added together using the + operator, and the result is stored in the z variable.

Functions

Functions are used to group a set of related statements that perform a specific task. Here's an example of how to create a function:

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scss
function sayHello() {
  alert("Hello World!");
}

In this example, the sayHello function is created, which displays an alert message with the text "Hello World!" when called.

Events

Events are actions or occurrences that happen in the browser, such as a button being clicked or a page finishing loading. JavaScript can be used to respond to these events and trigger specific actions. Here's an example of how to use an event to call a function:

php
<button onclick="sayHello()">Click me</button>

In this example, a button element is created with an onclick attribute that calls the sayHello function when the button is clicked.

Conditionals

Conditionals are used to execute different blocks of code based on whether a condition is true or false. Here's an example of how to use an if statement:

scss
var x = 10;
if (x > 5) {
  alert("x is greater than 5");
}

In this example, the if statement checks whether the variable x is greater than 5, and if it is, it displays an alert message with the text "x is greater than 5".

Loops

Loops are used to execute a block of code multiple times. JavaScript supports several types of loops, including for loops, while loops, and do-

What is a JavaScript Promise?

A JavaScript Promise is an object that represents a value that may not be available yet but will be at some point in the future. It has three states:

Pending: The initial state of a Promise. The operation represented by the Promise is not yet complete.
Fulfilled: The operation completed successfully, and the Promise has a resulting value.
Rejected: The operation failed, and the Promise has a reason for the failure.

javascript callback function

A javascript callback function is a function that is passed as an argument to another function and is executed inside that function. In other words, it is a function that is called back by another function.

Here's an example code snippet that demonstrates the use of a callback function:

javascript
function performOperation(callback) {
  console.log('Performing operation...');
  callback();
}

function callbackFunction() {
  console.log('Callback function called.');
}

performOperation(callbackFunction);

In this example, we define a function called performOperation that takes a callback function as an argument. Inside performOperation, we log a message to the console indicating that the operation is being performed, and then we call the callback function.

We also define a second function called callbackFunction that simply logs a message to the console.

When we call performOperation and pass callbackFunction as the callback function, performOperation logs a message to the console indicating that the operation is being performed, and then it calls the callbackFunction. The callbackFunction then logs a message to the console indicating that it has been called.

This is a basic example of how a callback function can be used in JavaScript to execute code after a particular operation has been performed.

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