正确使用Ajax成功吗？

Question

Why does my success function never runs?

JavaScript:

$.ajax({
    url: 'calculation.php',
    type: 'POST',
    dataType: "json",
    data: {
        data1: 2,
        data2: 3
    },
    success: function(result){
        alert(result);
    }
});

PHP:

if(isset($_POST["data1"])){
    $dataA = $_POST["data1"];
    $dataB = $_POST["data2"];
    if(dataA + dataB === 5){
        echo "success";
        $result = true; //I tried all 3 of these things which it seemed like others did but it still dosen't run.
        return $result;
    }
}

Answer 1

Try

echo json_encode("success");

You have set the data type to json so you have to return json.