Try this:
<!DOCTYPE html>
<html>
<head>
<script>
function checkedAll(e) {
var checkboxes = document.getElementsByTagName('input');
for (var i = 0; i < checkboxes.length; i++) {
if (checkboxes[i].type === 'checkbox') {
checkboxes[i].checked = e.checked;
}
}
}
</script>
</head>
<body>
<table>
<tr><input type="checkbox" onChange="checkedAll(this);" name="checkall">
Select All
</tr>
<tr>
<td width=10%><input name="chk1[]" type="checkbox" value="apple" >Apple</td>
</tr>
<tr>
<td width=10%><input name="chk1[]" type="checkbox" value="orange" >Orange</td>
</tr>
</table>
</body>
</html>