Can't get wordpress ajax form to submit - ajax

Question

I am porting an application to WordPress. It uses a form to select what attributes the customer is looking for in an Adult Family Home via checkboxes and drop-downs. It re-searches the database on each onchange and keyup. Originally I had the application standalone in PHP, but when I migrated it to WordPress I started having issues.
Currently in WP I have the code conditionalized ($DavesWay == 1) to do ajax the normal no-WordPress-way and ($DavesWay == 0) to do it the WordPress-way.
In the non-WordPress-way, the ajax works fine EXCEPT that I get a WP header and menu between the search form and the results-div that Ajax puts the data in. I get no errors from WP or in the JS console. In the WP-way The search form displayed, but nothing happens when I check any of the checkboxes. The JS console displays
POST http://localhost/demo4/wp-admin/admin-ajax.php 400 (Bad Request)
But I don't see any way to tell exactly what it is complaining about. How should I troubleshoot this?
Troubleshooting = Examine the HTML output, lots of echos and exits in PHP code, look at JS console.
function submitPg1(theForm) {
// Used with onChange from "most" form elements, but not on those that change the page
// rather than the select criteria. Such as rowsPerPage, pageNumber etc.
setById("pageNo", "1"); // set inital page
mySubmit();
}
function mySubmit(theForm) { // The actual ajax submit
// DO NOT set page number
jQuery.ajax({ // create an AJAX call...
data: jQuery("#asi_search_form").serialize(), // get the form data
type: jQuery("#asi_search_form").attr("method"), // GET or POST
url: jQuery("#asi_search_form").attr("action"), // the file to call
success: function (response) { // on success..
jQuery("#result").html(response); // update the DIV
}
})
}
function setById(id, value) { // Used to set vales by Id
x = document.getElementById(id).value;
x.value = value;
}
// 1st submit with blank selection
jQuery(document).ready(function () { submitPg1(this.form) });
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/1.12.4/jquery.min.js"></script>
Code fragments: (from the displayed page source)
<div id="asi_container" class="asi_container" >
<noscript><h2>This site requires Javascript and cookies to function. See the Help page for how to enable them.</h2></noscript>
<div id="searchForm">
<form id="asi_search_form" name="asi_search_form" method="post" action="http://localhost/demo4/wp-admin/admin-ajax.php">
<input type="hidden" name="action" value="asi_LTCfetchAll_ajax" style="display: none; visibility: hidden; opacity: 0;">
<table id="greenTable" class="asi_table" title="The Green areas are for site administration, not typical users">
<tbody>
PHP code:
$DavesWay = 0;
if ($DavesWay == 1){ //echo "Daves Way Setup"; // Dave's way, which works but prints the menu twice
if( $operation == "submit"){
require("asi_LTCfetchAll.php"); // for each onchange or onkeyup
}else{
add_filter( 'the_content', 'asi_tc_admin', '12' ); // Initial page refresh # must be >12
}
}else{
// The WordPress way that I could't get to work -- asi_LTCfetch never gets called
function asi_LTCfetchAll_ajax(){
//echo "<br /> Goto to Submit function"; // DEBUG
require($asi_plugin_dir . "/includes" . '/asi_LTCfetchAll.php');
}
add_action( "wp_ajax_asi_LTCfetchAll_ajax", "asi_LTCfetchAll_ajax" ); // admin users
add_action( "wp_ajax_nopriv_asi_LTCfetchAll_ajax", "asi_LTCfetchAll_ajax" ); // non-logged in users
add_filter( "the_content", "asi_tc_admin", "12" ); // Initial page refresh # must be >12
}

Answer 1

Try changing the JavaScript to the way WordPress recommends it in their documentation:
var data = {
'action': 'my_action',
'whatever': 1234
};
jQuery.post(ajaxurl, data, function(response) {
alert('Got this from the server: ' + response);
});

Answer 2

I suggest trying following URL: https://codex.wordpress.org/AJAX_in_Plugins
Also you can use the plugin: https://wordpress.org/plugins/ajax-search-lite/