MRcracker

const links = document.querySelectorAll('.navigation__link');

links.forEach(link => {
  const btn = document.createElement('button');
  btn.textContent = "BUTTON";

  link.appendChild(btn);
});

4.5.1. The a element
Content model:
Transparent, but there must be no interactive content or a element descendants.

Interactive content is content that is specifically intended for user interaction.
a (if the href attribute is present), audio (if the controls attribute is present), button, details embed, iframe, img (if the usemap attribute is present), input (if the type attribute is not in the Hidden state), label, select, textarea, video (if the controls attribute is present).
The tabindex attribute can also make any element into interactive content.

$name = basename($_POST['name']);
$textarea = $_POST['textarea'];

$file = __DIR__.'/files/'.$name;

//создаст файл или допишет данные в конец существующего
$fp = fopen($file, 'a+');
fwrite($fp, $textarea);
fclose($fp);

function click(e) {
  console.log(e.target.offsetWidth)
}

if (typeof isNumber == 'number') {
  return true;
} else {
  return false;
}

var btn = document.createElement("button");
btn.innerHTML = "кнопка";
document.querySelector("ul").insertBefore(btn,document.querySelector("ul>li.block"));

function getFiles($path,$lvl = 0){
	$res = [];
    $dir2 = scandir($path);	
    foreach($dir2 as $file2){
        if (($file2!='.') && ($file2!='..')){
			$fullpath = $path . DIRECTORY_SEPARATOR . $file2;
            if(is_dir($fullpath)){
				$res = array_merge($res,getFiles($fullpath,$lvl+1));
                array_push($res,["path"=>$fullpath,"name"=>$file2,"type"=>"DIR","level"=>$lvl,"size"=>filesize($fullpath)]);
            }else if(is_file($fullpath))
                array_push($res,[ "path"=>$fullpath,"name"=>$file2,"type"=>"FILE","level"=>$lvl,"size"=>filesize($fullpath)]);
		}
    }
	return $lvl == 0 ? array_reverse($res): $res;
}

function showFiles($arr){	
	foreach($arr as $v){
		$margin = $v["level"] * 15;
		
		if($v["type"] == "DIR")
			echo "<span style='display:block;font-weight:bold;margin-left:{$margin}px;'>$v[name]</span>";
		if($v["type"] == "FILE")
			echo "<a style='margin-left:{$margin}px;display:block;' href='$v[path]'>$v[name]  ($v[size] байт)</a>";
	}
}



showFiles(getFiles('yourdir'));

$b = [1,2,3,4,5,6,7,8,9];
$max = $b[0];
$c = count($b);
while($c-- > 0)
    $max = $b[$c] > $max?$b[$c]:$max;
echo $max;//9

$arr = [1, 2, 3];
$max = $arr[0];
$len = count($arr);

while ($len--) {
  if ($arr[$len] > $max) {
    $max = $arr[$len];
  }
}

echo $max;