Return Select option value in JavaScript

I'd like to return and output to a variable a select option that the user selects in a dropdown menu below.

<h3>Cake Size</h3>
<select id="cakeSize">
    <option value="6">6" Cake</option>
    <option value="8">8" Cake</option>
    <option value="10">10" Cake</option>
    <option value="12">12" Cake</option>
</select>
<button type="button" id="calc">Calculate</button>

I want to get 6/8/10/12 into a variable.

const calc = document.getElementById('calc');
let cakeSize = document.getElementById('cakeSize');
let value = cakeSize.value;

calc.addEventListener('click', function test(){
  return alert(value);
});

Would like to do this initially using a button event listener to trigger the collection of the value.

If you want to alert the selected value, use alert(cakeSize.value). let value = cakeSize.value; will have only the initial select value.

<!-- begin snippet: js hide: false console: true babel: false -->

<!-- language: lang-js -->

let cakeSize = document.getElementById('cakeSize');
// let value = cakeSize.value;

calc.addEventListener('click', function test() {
  return alert(cakeSize.value);
});

<!-- language: lang-html -->

<h3>Cake Size</h3>
<select id="cakeSize">
    <option value="6">6" Cake</option>
    <option value="8">8" Cake</option>
    <option value="10">10" Cake</option>
    <option value="12">12" Cake</option>
</select>
<button type="button" id="calc">Calculate</button>

<!-- end snippet -->