random number js min max

I'm trying to get random number between 2 numbers from input in JavaScript. When I put numbers instead of max.value and min.value it works, but not with variable. I can't understand how does random in js work, in other programming languages I know it's easy done like random(min,max) so I totally don't understand why is it so hard in JS. Thank you.

function genRanNumb() {
  document.getElementById('demo').innerHTML=Math.floor(Math.random()*(max.value-min.value+1)+min.value);
}

<input type="text" id="min">
<input type="text" id="max">
<button id="btn" onclick="genRanNumb()">button</button>
<p id="demo"></p>