jquery load passing a parameter - php

Question

Hello just want to ask what is the proper way to pass a parameter using jquery my parameter is from a html input , below is my code.
function ajax_post(){
var param = document.getElementById('def').value;
$('#chatlogs').load('main.php?id='+param);
}
I'm able to load the main.php but cannot get to echo the param, here is my main.php code.
<?php echo $_GET['id'];?>
Adding more details.. im getting the parameters from a HTML select input then after getting the value, will then load the main.php into a div with a id of #chatlogs.
<select name="topic" id="def" class="form-control" style="width:450px;" onChange='ajax_post()'>
<option value="" selected>---</option>
<option value="Solder Short">Solder Short</option>
<option value="Insufficient Solder">Insufficient Solder</option>
<option value="Misaligned Component">Misaligned Component</option>
<option value="Missing Component">Missing Component</option>
<option value="Inverted Component">Inverted Component</option>
<option value="Pad Contamination">Pad Contamination</option>
</select>
<div id="chatlogs">
Please select a defect category...
</div>

Answer 1

Try this:
<select name="topic" id="def" class="form-control" style="width:450px;">
<option value="" selected>---</option>
<option value="Solder Short">Solder Short</option>
<option value="Insufficient Solder">Insufficient Solder</option>
<option value="Misaligned Component">Misaligned Component</option>
<option value="Missing Component">Missing Component</option>
<option value="Inverted Component">Inverted Component</option>
<option value="Pad Contamination">Pad Contamination</option>
</select>
<div id="chatlogs">
Please select a defect category...
</div>
<script>
$(document).ready(function(){
$('#def').on('change', function() {
var param = document.getElementById('def').value;
//alert(param);
$('#chatlogs').load('main.php?id=', param);
})
});
</script>

Answer 2

Try this one:
function ajax_post(){
var param = document.getElementById('def').value;
$('#chatlogs').load('main.php?id='+param);
}