Difference between ES-5 and ES-6 and (Let,Var and Const)

Table-

Feature	ES5	ES6 (ES2015)
Variable Declaration	`var` is used for variable declaration.	`let` and `const` introduced for better variable scoping.
Block Scoping	Limited block scoping.	Improved block scoping with `let` and `const`.
Default Function Parameters	No support for default function parameters.	Supports default function parameters.
Arrow Functions	No arrow functions.	Arrow functions introduced for concise function syntax.
Template Literals	No template literals.	Supports template literals for string interpolation.
Rest Parameters	No rest parameters.	Rest parameters for gathering function arguments.
Spread Operator	No spread operator.	Spread operator for expanding elements in arrays or objects.
Classes	No classes, constructor functions used.	Introduces the `class` syntax for defining classes.
Inheritance	Prototypal inheritance pattern.	Improved inheritance with the `extends` keyword.
Modules	No native module system.	Introduces ES6 modules for better code organization.
Promises	No native Promise object.	Promises introduced for better asynchronous programming.
Generators	No generator functions.	Generator functions with the `function*` syntax.
Destructuring	No destructuring.	Destructuring syntax for assignment and extraction.
Maps and Sets	No native Map and Set objects.	Introduces native Map and Set objects for data structures.
Symbols	No native Symbol data type.	Introduces the Symbol data type for unique object properties.
Iterators and Iterables	No built-in support for iterators.	Introduces the concept of iterators and iterables.
Async/Await	No native async/await.	Introduces `async/await` for handling asynchronous code in a more readable way.
Array Methods	Arrays have methods like `forEach`, `map`, `filter`, etc.	Enhanced array methods like `find`, `findIndex`, and others.
String Methods	Limited built-in string methods.	Improved string methods like `startsWith`, `endsWith`, and others.
Object Literal Extensions	No shorthand for defining properties in object literals.	Shorthand property and method definitions.

let

Feature	`var`	`let`	`const`
Scoping	Function-scoped.	Block-scoped.	Block-scoped.
Hoisting	Hoisted to the top.	Hoisted to the top.	Hoisted to the top.
Reassignment	Allowed.	Allowed.	Not allowed.
Value Initialization	Not initialized (undefined).	Not initialized (undefined).	Must be initialized when declared.
Temporal Dead Zone	Not affected by temporal dead zone.	Affected by temporal dead zone.	Affected by temporal dead zone.
Redeclaration	Allowed.	Not allowed in the same scope.	Not allowed in the same scope.
Global Object Property	Creates properties on the global object.	Does not create properties on the global object.	Does not create properties on the global object.
Use Cases	Limited use due to hoisting issues.	Preferred for most cases with block scope.	Preferred for constants and when variable reassignment is not required.

It's important to note that choosing between var, let, and const depends on the specific use case and the desired behavior. let and const are generally preferred over var in modern JavaScript development because they offer better scoping and reduce common programming errors.

scope

Scope	Description	Example
Global Scope	Variables declared outside all functions.	`javascript let globalVar = 10;`
	Accessible from anywhere in the code.
	They have a lifetime of the entire
	program and persist until it ends.

Function Scope	Variables declared inside a function.	`javascript function foo() { let localVar = 5; }`
	Only accessible within that function.
	Local to the function and not visible
	outside.

Block Scope	Variables declared inside a block (e.g.,	`javascript if (true) { let blockVar = 20; }`
	within `if`, `for`, `while` statements).
	Limited to the block where they are
	declared.
	Introduced with ES6 (let and const).

Lexical Scope	Scope determined by the location of the	`javascript let x = 10; function outer() { let y = 20; function inner() { console.log(x, y); } inner(); }`
	variable's declaration within the code.
	Also known as "static scope."

In the example for lexical scope, the inner function can access variables from the outer and global scopes because of the way scopes are nested and determined by the structure of the code.

Global Scope:

javascriptCopy code// Global variable
let globalVar = 10;

function example() {
  // Access globalVar in the function
  console.log(globalVar);
}

example(); // Outputs: 10

In this example, globalVar is accessible within the example function because it's in the global scope.

Function Scope:

javascriptCopy codefunction foo() {
  // Local variable
  let localVar = 5;
  console.log(localVar);
}

foo(); // Outputs: 5

// Attempting to access localVar here will result in an error
// because it's not defined in this scope.

localVar is a local variable and can only be accessed within the foo function.

Block Scope (ES6 with `let`):

javascriptCopy codeif (true) {
  // Block-scoped variable
  let blockVar = 20;
  console.log(blockVar);
}

// Trying to access blockVar here will result in an error
// because it's not defined in this scope.

blockVar is scoped to the block defined by the if statement and cannot be accessed outside of it.

Lexical (Static) Scope:

javascriptCopy codelet x = 10;

function outer() {
  let y = 20;

  function inner() {
    console.log(x, y); // Accesses x from outer scope and y from its own scope
  }

  inner();
}

outer(); // Outputs: 10 20

In this example, inner can access x from the outer scope and y from its own scope. It uses lexical (static) scoping to resolve variable references.

These examples demonstrate how variables' scope works in JavaScript. Global variables are accessible anywhere, function scope restricts access to the function, block scope (with let) is confined to specific blocks, and lexical scope follows the nested structure of code.

complete

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Difference between ES-5 and ES-6 and (Let,Var and Const)

Global Scope:

Function Scope:

Block Scope (ES6 with let):

Lexical (Static) Scope:

Block Scope (ES6 with `let`):