Is the function a closure or not and why?

Question

The function counter can be a closure?

let count = 0;

function counter() {
  return count +=1;
}

console.log(counter()); // 1
console.log(counter()); // 2
console.log(counter()); // 3

Answer 1

The function counter can be a closure

Yes

closure is not only in nested function. The declaration of function in global scope is also a closure. According to MDN

A closure is the combination of a function and the lexical environment within which that function was declared

Answer 2

A closure is the combination of a function with references to its surrounding state (the lexical environment) combined together.

Every time you create a function you create a closure at function creation time

let count = 0;

function counter() {
  return count +=1;
}

console.log(counter()); // 1
console.log(counter()); // 2
console.log(counter()); // 3

Function counter doesn't define any variable count still has access to the count because count has been defined in the scope in which the closure was created.Additionally closures are capable of not only reading, but also manipulating the variables of their lexical environment which you are doing in your case.So precisely your function counter solely is a not a closure ,

function counter +its lexical environment is a closure