javascript - I declared my variable with let but it is still not in global scope

Question

I am trying to make a component appear on condition of 'uneligible=(age<18)' so I tried to declare uneligible out of his function's scope and declaring it with let because I know the value will change later

    let uneligible;
  const handleSaveGeneral = async (e) => {
    var dateOfBirth = "2007-01-01";
    var split_dob = dateOfBirth.split("-");
    var month = split_dob[1];
    var day = split_dob[2];
    var year = split_dob[0];
    var dob_asdate = new Date(year, month, day);
    var today = new Date();
    var mili_dif = Math.abs(today.getTime() - dob_asdate.getTime());
    var age = mili_dif / (1000 * 3600 * 24 * 365.25);
    console.log(age);
    uneligible = age < 18;
  };

now it's undefined in the syntax around the component and the component doesn't appear

<div>
      {uneligible && (
        <Alert variant="filled" severity="error">
          This is an error alert — check it out!
        </Alert>
      )}
    </div>

code sandox:https://codesandbox.io/s/serverless-wave-qyuc4?file=/src/App.js:602-767

I didn't use stateful variable because of that issue:conditional rendering is not working in my functional component

question from:https://stackoverflow.com/questions/65875644/i-declared-my-variable-with-let-but-it-is-still-not-in-global-scope

Answer 1

let allows you to declare variables that are limited to the scope of a block statement or expression on which it is used, unlike the var keyword, which declares a variable globally, or locally to an entire function regardless of block scope.

Just like const the let does not create properties of the window object when declared globally (in the top-most scope).

To achieve what you want you can use var / window.uneligible instead of let