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Javascript Variables

In JavaScript, Variables are used to store and manipulate data. They act as containers that hold values, which can be of different data types such as strings, numbers, booleans, objects, or arrays.


Variable Declaration and Initialization

To declare a Variable in JavaScript, you can use the var, let, or const keywords, followed by the variable name. Here's an example:


var age;
let name;
const PI = 3.14;

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Data Types and Dynamic Typing

JavaScript is a dynamically typed language, which means you don't have to explicitly specify the data type of a variable. It is determined automatically based on the value assigned to it. For example:


var message = "Hello"; // string
var count = 10; // number
var isTrue = true; // boolean

Assigning Values to Variables

You can assign values to Variables using the assignment operator (=). Here's an example :


var age = 25;
var name = "John";

Updating Variable Values

Once a Variable is declared and assigned a value, you can update its value by assigning a new value to it. Here's an example :


var count = 5;
count = count + 1; // updated value: 6

In the example above, the variable count is initially assigned the value of 5. The next line of code updates the value of count by adding 1 to its current value. The comment "// updated value: 6" explains that the new value of count after the update operation is 6.


Variable Scope and Hoisting

JavaScript has both global and local variable scopes. Variables declared outside any function have a global scope, while variables declared within a function have a local scope.
Variable hoisting is a JavaScript behavior where variables declared with var are moved to the top of their scope. Here's an example :


console.log(age); // Output: undefined
var age = 30;


Constants and Immutable Variables

In JavaScript, You can declare constants using the const keyword. Constants are variables that cannot be reassigned. when you declare a variable using the const keyword, it creates a constant variable whose value cannot be changed or reassigned. If you try to assign a new value to a constant variable, you will encounter a runtime error, and the JavaScript engine will throw an error similar to "// Error: Assignment to a constant variable".
Here's an example:


const PI = 3.14;
PI = 3.14159; // Error: Assignment to a constant variable

In the example above, attempting to assign a new value to the PI constant will result in an error because constants are meant to be immutable and cannot be changed after declaration.


Remember to use meaningful variable names, follow naming conventions, and be consistent in your code. Understanding variables is fundamental to JavaScript programming, as they allow you to store and manipulate data throughout your code.