如何使用JavaScript获取列表项中的第一个和最后一个元素

Question

<script>
    function editMediaInfo(mediaID){
        var nex = document.getElementById(mediaID).nextElementSibling.nextElementSibling.id;
        alert(nex);
        console.log(nex);
    }
</script>

<?php
$x = 1;
echo "<ul>";

while($x <= 5)
{
    echo "<li id={$x}> item {$x} </li>";    
    ?>
    <button onclick="editMediaInfo('<?php echo $x; ?>')">Click</button>
    <?php
    $x++;
}

echo "</ul>";   
?>

When I click any button (except item 5) it gives me an alert with next id element and this normal what I need here to do that when I click button item 5 give me another alert I tried to do this but every time console give me this message:

Uncaught TypeError: Cannot read property 'id' of null  

Answer 1

Get the Id of the element if only it exists! I've added the if condition for that.

function editMediaInfo(mediaID){
var nex =   document.getElementById(mediaID).nextElementSibling.nextElementSibling;
var nextId="";
if(nex!=null){
  nextId=nex.id;
  alert(nextId);
}
else{
alert("no next element");
}
console.log(nextId);
}