How to call a PHP function in JavaScript?

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']);
?>

Answer 2

You won't be able to do this in the way you might be expeting to. PHP is executed on the server, before the browser receives the HTML. On the other hand, JavaScript runs in the browser and has no knowledge of the PHP (or any other server side language) used to create the HTML.

To "call" a php function, you have to issue a request back to the server (often referred to as AJAX). For example, you could have a checkYear.php script which checks the event and returns some HTML indicating whether the check succeeded. When the HTML fragment gets back to the JavaScript, you inject it into the page.

Hope this helps!