why input value cannot be access inside function in javascript [duplicate]

Question

Why the variable is empty when accessing inside a function? Please see my code below

var age = document.getElementById('ageValue').value

function getAge() {
    document.getElementById('age').innerHTML = 'Your age is: ' + age
}

<div id="age"></div>

<input type="text" id="ageValue">

<button type="button" onclick="getAge()">Show Age</button>

Answer 1

Put the reading the age part inside the function.

function getAge() {
    var age = document.getElementById('ageValue').value;
    document.getElementById('age').innerHTML = 'Your age is: ' + age
}

<div id="age"></div>

<input type="text" id="ageValue">

<button type="button" onclick="getAge()">Show Age</button>