Question

I have

index.php

<select id="year_list" name="year_list" onchange="check_year_event('year_list', 'event_list');" > . . .  </select>

<select id="event_list" name="event_list" onchange="check_year_event('year_list', 'event_list');" > . . . </select>
.
.
.
<?php 
 function checkYearandEvent($year, $event) {
  $year_event = mysql_query("SELECT * FROM year_event WHERE year = '$event' AND event = '$event'")

  if (mysql_num_rows($year_event) > 0) {
   // do this
  }

 }
?>

myscripts.js

function check_year_event(year_id, event_id) {
 var year = document.getElementById(year_id).value;
 var event = document.getElementById(event_id).value;

 // call PHP function (but I don't know how): checkYearandEvent(year, event);

}

My question is how do I call the PHP function every time the user changes the value of any of the select element.

Answer 1

You need to use ajax. There is a basic example:

myscripts.js

function AjaxCaller(){
    var xmlhttp=false;
    try{
        xmlhttp = new ActiveXObject("Msxml2.XMLHTTP");
    }catch(e){
        try{
            xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");
        }catch(E){
            xmlhttp = false;
        }
    }

    if(!xmlhttp && typeof XMLHttpRequest!='undefined'){
        xmlhttp = new XMLHttpRequest();
    }
    return xmlhttp;
}

function callPage(url, div){
    ajax=AjaxCaller(); 
    ajax.open("GET", url, true); 
    ajax.onreadystatechange=function(){
        if(ajax.readyState==4){
            if(ajax.status==200){
                div.innerHTML = ajax.responseText;
            }
        }
    }
    ajax.send(null);
}

function check_year_event(year_id, event_id) {
 var year = document.getElementById(year_id).value;
 var event = document.getElementById(event_id).value;

    callPage('file.php?year='+year+'&'+'event=+'+event,document.getElementById(targetId));
}

file.php

<?php 

     function checkYearandEvent($year, $event) {
      $year_event = mysql_query("SELECT * FROM year_event WHERE year = '$event' AND event = '$event'")

      if (mysql_num_rows($year_event) > 0) {
       // do this
      }

     }
    echo checkYearandEvent($_GET['year'], $_GET['event']);
?>