In JavaScript, "let" and "var" are used to declare variables, but they differ in their scoping and hoisting behavior.

Scope: The scope of a variable refers to the part of the program where it can be accessed. Variables declared with "var" are function-scoped, which means they are accessible throughout the function in which they are declared, including any nested functions. On the other hand, variables declared with "let" are block-scoped, which means they are only accessible within the block in which they are declared (i.e., within curly braces {}).
For example:

function myFunction() {

  var x = 10;

  if (true) {

    var x = 20;

    console.log(x); // outputs 20

  }

  console.log(x); // outputs 20

}


function myFunction() {

  let x = 10;

  if (true) {

    let x = 20;

    console.log(x); // outputs 20

  }

  console.log(x); // outputs 10

}

In the first example, the variable "x" is function-scoped, so the inner declaration of "x" with "var" overrides the outer declaration. In the second example, the variable "x" is block-scoped, so the inner declaration of "x" with "let" creates a new variable that only exists within the block.

Hoisting: Hoisting refers to the behavior of moving variable and function declarations to the top of their respective scopes before any code is executed. Variables declared with "var" are hoisted to the top of their function scope, while variables declared with "let" are not hoisted.
For example:
function myFunction() {

  console.log(x); // outputs undefined

  var x = 10;

}


function myFunction() {

  console.log(x); // throws a ReferenceError

  let x = 10;

}

In the first example, the declaration of "x" with "var" is hoisted to the top of the function, so it exists but has no value yet. In the second example, the declaration of "x" with "let" is not hoisted, so an error is thrown when trying to access it before it is declared.

In summary, "let" and "var" differ in their scoping and hoisting behavior. "var" is function-scoped and hoisted, while "let" is block-scoped and not hoisted. It is generally recommended to use "let" instead of "var" for better scoping and to avoid potential bugs.