JavaScript(JS) let

let is a keyword in JavaScript introduced in ES6 (ECMAScript 2015) that is used to declare a block-scoped variable.

Unlike the var keyword, which declares variables with function-level scope or global scope, let allows you to declare variables with block-level scope. This means that variables declared with let are only accessible within the block they are declared in, including inner blocks, and are not hoisted to the top of the scope like var variables are.

Here's an example of using let to declare a variable with block-level scope:

function foo() {
  let x = 10;
  if (true) {
    let x = 20; // this variable only exists within the block
    console.log(x); // 20
  }
  console.log(x); // 10
}

In this example, the let keyword is used to declare two variables with the same name x. However, since the let variables have block-level scope, they are separate variables and changing the value of x inside the inner block does not affect the value of x in the outer block.

Using let can help prevent errors caused by variable shadowing and make it easier to reason about the code by clearly defining the scope of variables.