Clean Code in JavaScript

Let declarations

Let declarations are thankfully far simpler than var declarations. They will be scoped to their nearest environment (whether it is a block, a function, a module, or the global environment) and have no complicated hoisting behaviors.

Their ability to be scoped to a block means that a let declaration inside a block will not have an effect on the outer function scope. In the following code, we can see three different environments (scopes) with a respective place variable in each:

let place = 'outer';function foo() {  let place = 'function';  {    let place = 'block';    place; // => "block"  }  place; // => "function"}foo();place; // => "outer"

This demonstrates two things to us:

• Declaring via let will not overwrite or mutate a variable ...