JShint：期望一个赋值或函数调用，而是看到一个表达式(JShint :Expected an assignment or function call and instead saw an expression)

 不要从其他文件修改PHP脚本 - 这是一个坏主意。 
 有更好的解决方案 - 幸运的是简单的解决方案。 从URL字符串中获取用户需要的内容。 查询位于$_GET全局数组中。 
 
//default sort values
$sortby = "Price";
$order = "DESC";
if(isset($_GET['sortby'])){ //if theres a sortby query in the URL
    $sortby = mysql_real_escape_string($_GET['sortby']);
}
if(isset($_GET['order'])){ //if user provided elements order in the URL
    $order = mysql_real_escape_string($_GET['order']);
    if($order == "DESC"){
        $order = "DESC";
    }else{
        $order = "ASC";
    }
}


$db_handler = new DB();
$query = "SELECT `Title`, `Autor`, `Price`, `Cover`, `Brief_desc`, `id` FROM `book` ORDER BY $sortby $order";
 
 这个例子的一个注释： 总是使用ESCAPING ！ （mysqli_real_escape_string更好，但需要mysqli链接（引用你的数据库，我没有一个，我不知道你的数据库类提供了什么方法，变量））。 
 他们阻止你进行SQL注入 
 
 链接将是 
 
<a href="index.php?sort=Price&order=ASC">Sort from least exspensive</a> 
<a href="index.php?sort=Price&order=DESC">Sort from most exspensive</a>

Dont ever modify php scripts from other files - thats a bad idea.
 There are better solutions - Fortunately the simple ones. Just get what user need from URL string. The queries are in the $_GET global array. 
 
//default sort values
$sortby = "Price";
$order = "DESC";
if(isset($_GET['sortby'])){ //if theres a sortby query in the URL
    $sortby = mysql_real_escape_string($_GET['sortby']);
}
if(isset($_GET['order'])){ //if user provided elements order in the URL
    $order = mysql_real_escape_string($_GET['order']);
    if($order == "DESC"){
        $order = "DESC";
    }else{
        $order = "ASC";
    }
}


$db_handler = new DB();
$query = "SELECT `Title`, `Autor`, `Price`, `Cover`, `Brief_desc`, `id` FROM `book` ORDER BY $sortby $order";
 
One note for this example: ALWAYS USE ESCAPING! (The mysqli_real_escape_string is better, but requires mysqli link (reference to your db, i dont have one and i dont know what methods,variables your DB class provides)).
 They are preventing you from SQL Injection
 
Links will be
 
<a href="index.php?sort=Price&order=ASC">Sort from least exspensive</a> 
<a href="index.php?sort=Price&order=DESC">Sort from most exspensive</a>