multiple checkbox save to database

index.php

index.php

<script type="text/javascript">
function save(){
	var formdata = $('#frm').serialize();
	$.ajax({
		url: "save.php",
		type: "POST",
		data: formdata,
		success: function(result){
			console.log(result);
		}
	});

}
</script>
<form method="POST" name="fmr" id="frm">
<input type="checkbox" name="chk[]" id="chk" value="A"> A<br>
<input type="checkbox" name="chk[]" id="chk" value="B"> B<br>
<input type="checkbox" name="chk[]" id="chk" value="C"> C<br>
<input type="checkbox" name="chk[]" id="chk" value="D"> D<br>
<input type="checkbox" name="chk[]" id="chk" value="E"> E<br>
<input type="button" value="Submit" class="submit" onclick="save()">
</form>



save.php
$chk =  $_POST['chk'];
echo implode("|", $chk);
output: A|B|C