let declared variable can be declared or not

Question

I am getting

Uncaught Syntax Error: Identifier 'a' has already been declared

can any one tell me why ?

 let a = 3; function a() { let a = 1; } console.log(a); a(); 

Answer 1

let makes a variable block scoped. All blocks opened within a block wherein a is declared know a .

Additionally, your first a and the function a are colliding.

Answer 2

Basically you did this:

let a = function () {
  let a = 1;
}

let a = 3; // At this point you already have 'a' variable

Answer 3

First of all, you're creating a function with the same name as an already created variable 'a', whether you can or not you really should never do that.

Secondly let allows you to declare variables that are limited in scope to the block, statement, or expression on which it is used. This is unlike the var keyword, which defines a variable globally, or locally to an entire function regardless of block scope. In other words, your function already has the variable 'a' declared.