Select Multiple, maar dan met een maximum

<script>
function check(obj)
{
	tel = 0;
	y = obj.options.length;
	for(x=0;x<y;x++)
	{
		if(obj.options[x].selected)
		{
			tel++;
		}
	}
	if(tel > 2)
	{
		alert("Je hebt te veel Options geselecteerd.");	
	}
}
</script>
<select multiple="multiple" onchange='check(this)'>
...
</select>

<script>
function check(obj)
{
	tel = 0;
	y = obj.options.length;
	for(x=0;x<y;x++)
	{
		if(obj.options[x].selected)
		{
			tel++;
		}
	}
	if(tel > 2)
	{
		alert("Je hebt te veel Options geselecteerd.");	
	}
}
</script>
<select multiple="multiple" onchange='check(this)'>
...
</select>

<script>
function del(veld)
{
    document.all.veld.value = "";
}
</script>
<input type="text" name="blaat" /><br />
<input type="button" onClick="del('blaat')" value="del" />

<script>
function del(veld)
{
    document.all.veld.value = "";
}
</script>
<input type="text" name="blaat" /><br />
<input type="button" onClick="del('blaat')" value="del" />

<script>
function del(obj)
{
    y = obj.options.length;
    for(x=0;x<y;x++)
    {
        obj.options[x].selected = false;
    }
}
</script>
<select multiple="multiple" id=select_name'>
...
</select>
<input type='button' onclick='del(document.getElementById("select_name"));'>

<script>
function del(obj)
{
    y = obj.options.length;
    for(x=0;x<y;x++)
    {
        obj.options[x].selected = false;
    }
}
</script>
<select multiple="multiple" id=select_name'>
...
</select>
<input type='button' onclick='del(document.getElementById("select_name"));'>

<script>
function del(veld)
{
    document.getElementById(veld).selectedIndex = -1;
}
</script>
<select id='test' multiple="multiple">
...
</select>
<input type="button" onClick="del('test')" value="del" />

<script>
function del(veld)
{
    document.getElementById(veld).selectedIndex = -1;
}
</script>
<select id='test' multiple="multiple">
...
</select>
<input type="button" onClick="del('test')" value="del" />