Ajax转PHP失败

My Ajax script keeps returning a result of unsuccessful. The console doesn't appear to show any errors. It just keeps throwing the alert window saying "error" instead of showing the result.

Ajax

$.ajax
({
  url: 'query.php',
  type: 'POST',
  dataType:'json',
  data: {Category: 'test'},
  success: function(result) 
  {    
    if(result) 
    {          
      console.log(result);
      alert(result);
    }
  },
  error: function() 
  {
    alert("error");
  }      
}); // end ajax call

php

$cat = $_POST['Category'];
echo $cat;

jquery ajax document

option 1

response a json from php

example: echo "{}";

option 2

remove dataType: 'json'

please check your query.php page. and make sure this page return some response either data or error massage like statusText="Error".

Do ajax function like below

$.ajax({ url: 'query.php',
type: 'POST',
dataType:'json',
data: {Category: 'test'},
success: function(result) 
{
if(result.success=="TRUE")
{
console.log(result);
alert(result.cat);
}
},
error: function()
{
alert("error");
}
});

In query.php

$cat=$_POST['category'];
if(!empty($cat)){
$data['success']="TRUE";
$data['message'] = "Category Found.";
$data['cat']='$cat';
}
else{
$data['success'] = "False";
$data['message'] = "Category not found.";
}
die(json_encode($data));