# Introduction to JavaScript

JavaScript is a versatile programming language used for web development. It enhances websites with dynamic and interactive elements, such as form validation, DOM manipulation, and animation. JavaScript is essential for modern web development and Its extensive library ecosystem and community support make it a top choice for modern web development. In this article, we will learn some basic fundamental concepts of JavaScript, Let's dive in and explore the exciting possibilities of JavaScript programming.

## **What is JavaScript ?**

* General-purpose & high-level programing language.
    
* Single-threaded synchronous programing language.
    
* Multi-paradigm programing language.
    
* Prototype-based, object-oriented programing language
    
* Just-in-time compiled programming language.
    

## **Identifiers and Keywords**

* Identifiers are names used to identify variables, functions, objects, or any other user-defined entity.
    
* Keywords are similar to identifiers but it has some special meaning.
    
* Keywords are the reserved words in a programming language.
    
* It can't be used as a variable name and function name
    

> ***e.g*** `var`, `let`, `const`, `if`, `return`, `this`, etc

## **Semicolon**

* Every Statement is terminated with a semicolon `;`
    
* It's optional to use.
    

## Comment

* It is used for documentation purposes and avoided by the compiler
    
* Single-line comment
    

```javascript
// This is a single-line comment
```

* Multiple line comment
    

```javascript
/*
This is a 
multi-line 
comment
*/
```

## **Output**

* It is the result of the program which is displayed to the user.
    
* In JavaScript, There are several ways to print output.
    
    1. using `console.log()`
        
    2. using `document.write()`
        
    3. using `alert()`
        
    
    ### **1\. Using Console.log()**
    
    * It is a method used to output data or messages to the browser console.
        
    * The `log()` part of `console.log()` is a function call that accepts one or more arguments to be printed to the console.
        
    * The `console.` part of `console.log()` is an object reference that provides access to the `log()` method.
        
        **Example**
        
        ```javascript
        console.log("Hello");
        console.log("Everyone");
        ```
        
        **Output**
        
        ```javascript
        Hello
        Everyone
        ```
        
    
    ### **2\. Using document.write()**
    
    * It is a method used to write dynamic content to an HTML document.
        
    
    #### **Example**
    
    ```javascript
    <!DOCTYPE html>
    <html>
      <head>
        <title>Shubham Jha</title>
      </head>
      <body>
        <script>
          document.write("<h1>Hi Welcome </h1>");
        </script>
      </body>
    </html>
    ```
    
    ### **3\. Using alert()**
    
    * It is a method used to display output as a pop-up message.
        
    
    #### **Example**
    
    ```javascript
    alert("Hello, world!");
    ```
    

## **Input**

* Using the `prompt()` method, we can take user input.
    
* It only takes a string as its argument.
    

#### **Example**

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

#### **Output**

```javascript
What is your name?> Shubham
Hello, Shubham!
```

## **Values & Types**

* A Value represents a piece of data in JavaScript and different representations of value are called types.
    
    1. Number Types: A numerical value, such as `34`, `-6.14`, `84`
        
    2. Boolean Types: true and false
        
    3. String Types: `"name"`
        
    4. Undefined Types
        
    5. Null Types
        
    6. Symbol Types
        
    7. Object Types
        

## Variables

* A variable is a container that stores a value.
    
* Two types of variables exist
    
    * Static Type: Values of fixed type are stored in a variable of fixed type.
        
    * Dynamic or Weak Type: Any type of value is stored in a variable.
        
* JavaScript supports weak or dynamic typed variables, so we don't have to declare the type of variable, It can store any type of variable.
    

### Variables Declare

* Variables are created by using the `let`, `const`, or `var` keywords.
    

#### **Example**

```javascript
var userName;
let age;
```

### **Variables Initialize**

* Assign the value to the variables
    

#### **Example**

```javascript
var userName = "shubham";
let age = 18;

console.log(userName);
console.log(age);
```

#### **Output**

```javascript
shubham
18
```

### **Variables Update**

* update the assigned value of the variable
    
    > `var` and `let` can be updated
    

#### **Example**

```javascript
var userName = "shubham";
console.log(userName);

userName = "developer";
console.log(userName);
```

**Note**

> `var` can be updated and re-declared
> 
> `let` can be updated but not re-declared

### **Variable using const**

* It is used to declare a constant variable that cannot be reassigned.
    
* It must be initialized with some value
    
* It can't be updated or re-declared
    

#### **Example**

```javascript
const userName = "shubham";
console.log(userName);
```

## **Happy Reading ! 😊**