AJAX不返回任何数据

Question

still fairly new to AJAX. I feel I'm not grasping it completely. I want to submit partial data to the server, perform an SQL query and return the results. This is what I have so far:

jQuery

j$('select[name=agent_Name]').change(function(event) {
     event.preventDefault();
     var agentID = j$(this).val();
     post_data = {'agent_ID':agentID};
     console.log("About to post data to the server");
    j$.post('../include/booking_Modify.php', post_data, function(response){  
        if(response.type == 'AgDEpCd'){
            output = response.text;
            console.log(output);
        }
        if(response.type == 'error'){
            output = response.text;
            console.log(output);
        }
    }, 'json');     
});

PHP

<?php
session_start();
require("../include/conn.php");
dbopen();
//check $_POST vars are set, exit if any missing
    if(!isset($_POST["agent_ID"]))
    {
        $output = json_encode(array('type'=>'error', 'text' => 'Nothing was selected!'));
        die($output);
    }

    $stmt = $conn->prepare("SELECT AgDEpCd FROM AGENTS WHERE AgentID = ?");
    $stmt->bind_param('i', $_POST["agent_ID"]);   // bind variables to the parameter
    $stmt->execute();

    $row = $result->fetch_assoc();
    $AgDEpCd = $row['AgDEpCd'];
    $stmt->close();
    $output = json_encode(array('type'=>'AgDEpCd', 'text' => $AgDEpCd));
    die($output);
?>

I checked to make sure: the file path was correct. var agentID = j$(this).val(); actually grabs a value, which it does Manually entered the SQL query into PHPMyAdmin to ensure I was retrieving results. I can't seem to return anything from the server. I'm not sure this is even possible. Please help!

Answer 1

Normally I will do just echo and exit, short and faster. In beforehand entering response, just console.log and check out if it return any. If it doesn't just check your php code, there is other error than the encoding output. Try it.

 <?php
    session_start();
    require("../include/conn.php");
    dbopen();
    //check $_POST vars are set, exit if any missing
        if(!isset($_POST["agent_ID"]))
        {
            echo json_encode(array('type'=>'error', 'text' => 'Nothing was selected!'));
            exit;
        }

        $stmt = $conn->prepare("SELECT AgDEpCd FROM AGENTS WHERE AgentID = ?");
        $stmt->bind_param('i', $_POST["agent_ID"]);   // bind variables to the parameter
        $stmt->execute();

        $row = $result->fetch_assoc();
        $AgDEpCd = $row['AgDEpCd'];
        $stmt->close();
        echo json_encode(array('type'=>'AgDEpCd', 'text' => $AgDEpCd));
        exit;
    ?>