Ajax JavaScript的PHP

I'm going to ask a question that has been mentioned very often but I can't understand what is missing in my code to make it work. I have two PHP files, one that acts as a viewer and the other one that processes, performs processes and a javascript file where I put my ajax requests. My goal is simple to pass a variable between my Js and my PHP.

My global.js file

  window.onload = function(){
      
      
   
   
      for($i = 0; $i <= 0; $i++){
          console.log("after for");
          console.log($i);
   $input = document.getElementsByClassName('from_1')[$i].textContent;
   $sub = document.getElementsByClassName('subject_1')[$i].textContent;
   $recei = document.getElementsByClassName('received_1')[$i].textContent;
   $preview = document.getElementsByClassName('bodypreview_1')[$i].textContent;
   $body_1 = document.getElementsByClassName('body_1')[$i].textContent;
    console.log("*********************");
    console.log($input);
    console.log($sub);
    console.log($recei);
    console.log($preview);
    console.log($body_1);
    console.log("*********************");
    
    
}};

I recover data with getElementsById and store it in variables. Then in the same file I make my Ajax call

function btn_urgent(html){
    console.log("*************************");
    console.log("btn_urgent");
    console.log($input);
    console.log("*************************");
    $.ajax({url: '../../wp-content/plugins/game_plugin/process_general.php',
        
    type: 'POST',
    
    data: {info: 'insert_to_db', $input: $input},
    
    success: function(output) {
        console.log("*************************");
            console.log("ssrtsgsgsg");
             alert(output);
             
             
            console.log("*************************");
            return($input);
            
             
        }

In my game. php file I have an onclick that calls my function "btn_urgent".

<button type="submit"  class="btn btn-primary col-2" onclick="btn_urgent()" >urgent</button>

Once my Ajax function is called it calls another function insert_to_db in the process_general file.

 function insert_to_db($input){
     
global $wpdb;
echo json_encode;
         $wpdb->insert(
                    'test_insert', //table name
                    array(
                'id' => 550,
                'from_mail' => $input,
                
                    ), //columns
                    array(
                '%d',
                '%s',
               
                    )
            );

     
  }

As you can see I'm trying to make a $input insert when I click my onclick. but it doesn't work. On the other hand my function insert_to_db is well called by my Ajax request but it does not pass $input. I think I'm forgetting something in the success story, but I don't know what. If someone has a few tips solution to offer me I am a buyer. I don't know how important this is, but I'm getting into wordpress. I remain available if necessary, thank you all and have a good day.

</div>

On your ajax data, it have invalid field name:

data: {info: 'insert_to_db', $input: $input},

Change to this:

data: {info: 'insert_to_db', input: $input},

on your php, you need grab the data like this:

$info = $_POST['info'];
$input= $_POST['input'];
// Then call the function
insert_to_db($input)