What are variables in javaScript

In JavaScript, variables are used to store data values. They act as containers for storing information that can be referenced and manipulated throughout a program. Variables in JavaScript are declared using keywords such as var, let, or const.

Declaration of Variables:

  1. var (ES5):
    • Declares a variable that is function-scoped.

                        var myVar = 'Hello';

  2. let (ES6+):
    • Declares a block-scoped variable that can be reassigned.

                        let age = 25;
                        age = 30; // Can be reassigned                    

  3. const (ES6+):
    • Declares a block-scoped variable that cannot be reassigned. However, for objects and arrays, their properties and elements can be modified.

                        const pi = 3.14;

Characteristics of Variables:

  1. Naming Rules:
    • Variable names in JavaScript must begin with a letter (a-z, A-Z), underscore (_), or dollar sign ($) and can contain letters, digits, underscores, or dollar signs.
    • They cannot use reserved keywords.
  2. Data Types:
    • Variables in JavaScript can hold different types of data: numbers, strings, booleans, objects, arrays, functions, etc.
  3. Scope:
    • var has function-level scope, while let and const have block-level scope (inside curly braces {} ).
  4. Hoisting:
    • var variables are hoisted (moved to the top of their scope) and initialized with undefined before the code is executed.
    • let and const are also hoisted but not initialized, resulting in a "Temporal Dead Zone" where accessing them before declaration causes a ReferenceError.

Example Usage:

            // Variable declarations
            var name = 'Alice';
            let age = 30;
            const PI = 3.14;
            // Usage
            console.log(name); // Output: Alice
            age = 35; // Reassigned value
            console.log(age); // Output: 35
            // Constants cannot be reassigned
            // PI = 3; // This would throw an error
            // Data types in variables
            let isStudent = true;
            let scores = [90, 85, 78];
            let person = { firstName: 'Bob', lastName: 'Smith' };            

Variables in JavaScript are fundamental for storing and manipulating data, and their behavior differs based on their declaration (var, let, const) and scope within the code.

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