check if input is between two int or float then display or not display content

In javascript I need to check whiwh value user enter in an html input like this:

<input type="text" id="volume" class="form-control" name="voilume"></input>

<div id"button"></div>

Ineed to know if the input is between 0,5 and 8 (so I have int and float as you can understand).

So the value has to be >= 0,5 and <= 8

If value input if between 0,5 and 8 I have to display a button, else nothing to do. But I need to prevent if user change the value many times.

So if he enters 3 display a button in div id=button", if it changes for another value like 2 for example keep displaying the button, but if he changes value input for 100 I need to remove the button in div id="button".

for now I tried something like this in order to test if it works:

var input= $('#volume').val();
    if (input >= 0.5 && input <= 8) {
        $('#button').html('ok');
    } else {
      $('#button').empty();
    }

But it does not work.