错误：调用Ajax时出现未定义索引

Question

The problem that I'm facing is that I'm getting an Undefined Index variable while calling Ajax. I need to post "json" data to the "update.php" page on click of submit button. Basically, I need to capture the values in textbox and send it to the database.

so, I have created a form on the submit button, for which the code is below:

<form action="update.php" method = "post" class="form-inline">
    <input type="submit" class="btn btn-info" id = "saveEdits" disabled = "disabled" onclick = "updateVal()" name="saveEdits"  value="Update"/>
/form>

This submit button Calls for an UpdateVal function that captures the value on the text-boxes shown on the page and using AJAX send it to the another php page.

updateVal function is as below:

function updateVal() {

    var node_list = document.getElementsByTagName('input');
    var c = 0;
    var fieldName = [];
    var fieldText = []
    var ID = [];
    for (var i = 0; i < node_list.length; i++) {
        var node = node_list[i];
        if (node.getAttribute('type') == 'text') {
            fieldName[c] = node.name;
            fieldText[c] = node.value;
            ID[c] = node.id;
            c++;
        }
    }
    var postData = {
        fieldName: fieldName,
        fieldText: fieldText,
        ID: ID
    };

    $.ajax({
        type: "post",
        url: "update.php",
        dataType: "json",
        data: {'postData' : JSON.stringify(postData)},
        contentType: 'application/x-www-form-urlencoded; charset=UTF-8'
    });

The run time data ie value in textboxes is being captured and can be shown at console, however, when I'm posting this data on update.php, where I would be capturing the json and will update the database, I'm getting the error:

Notice: Undefined index: in update.php on line 11

Below is my update.php

<?php
$json = $_POST["postData"];
$result = json_decode($json);
var_dump($result);?>

Answer 1

Remove your action attribute from your form, since you send your data per Javascript/AJAX you don't need it.

What you do now is: you send the data twice, once per updateVal() and once per default submit handling of the form.

Since the form-submitted data doesn't contain a input named postData , you are getting your undefined index error.

Edit: You stated you are not comfortable with the whole AJAX topic. Here is a nice simple answer covering the basics.

Edit2:

to listen for the response of your server add a callback to your ajax-request:

$.ajax({
    type: "post",
    url: "update.php",
    dataType: "json",
    data: {'postData' : postData},
    contentType: 'application/x-www-form-urlencoded; charset=UTF-8'
}).done(function (response, textStatus, jqXHR){
    // Show an alert on response
    alert(response);
});