<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
</head>
<body>
<form>
<select name="" id="lista" multiple>
<option>jeden</option>
<option>dwa</option>
<option>trzy</option>
</select>
<input type="button" value="Lista" onclick="funk()">
</form>
<p id="wynik"></p>
<script>
function funk()
{
var l = document.getElementById("lista");
document.getElementById("wynik").innerHTML = "";
for(var i=0; i <l.options.length; i++)
{
if(l.options[i].selected)
document.getElementById("wynik").innerHTML += l.options[i].value+" ";
}
}
</script>
</body>
</html>