In javascript, What is the difference between let and var?

In JavaScript, "let" and "var" are both used for declaring variables, but they have some differences in how they work and how they can be used.

Some of the key differences is below:

• Scope: The main difference between "let" and "var" is their scope. Variables declared with "var" have function scope or global scope, while variables declared with "let" have block scope. This means that a variable declared with "var" is visible throughout the entire function, while a variable declared with "let" is only visible within the block it is declared in.
• Hoisting: Variables declared with "var" are hoisted to the top of their scope, which means they are available throughout the entire function even if they are declared later in the code. Variables declared with "let" are not hoisted and cannot be accessed before they are declared.
• Reassignment: Variables declared with "var" can be reassigned to a new value, while variables declared with "let" can also be reassigned, but they cannot be redeclared in the same scope.
• Use in loops: When used in a loop, "var" and "let" have different behaviors. Variables declared with "var" have function scope and are shared across all iterations of the loop. Variables declared with "let" have block scope and are re-declared for each iteration of the loop.

Here is an example to illustrate the difference:

function example() {
  var x = 10;
  let y = 20;
  if (true) {
    var x = 30; // This reassigns the same variable declared earlier
    let y = 40; // This declares a new variable with the same name but within a different block
    console.log(x); // Output: 30
    console.log(y); // Output: 40
  }
  console.log(x); // Output: 30
  console.log(y); // Output: 20
}

In this example, the "var" variable "x" is re-assigned within the block, and its new value is visible outside the block. The "let" variable "y" is also declared within the block, but it is not visible outside the block.