js processing events for previous and next years

Processing the information of the previous and next month and the previous and next year

Add one after December to become January and add 1# to the year

##One month before subtracting one is December and the year should be subtracted by one

<?php
$prey=$nexty=$year;
$prem=$nextm=$mon;
if($prem<=1){
$prem=12;
$prey--;
}else{
$prem--;
}
if($nextm>=12){
$nextm=1;
$nexty++;
}else{
$nextm++;
}
$prey=$year-1;//上一年
$nexty=$year+1;//下一年
//超链接
echo "<tr><td colspan='7'align='center'>";
echo "<a href='sy1.php?y={$prey}'><<</a> ";
echo "<div>{$year}年</div>";
echo "<a href='sy1.php?y={$nexty}'>>></a>  ";
echo " ";
echo "<a href='sy1.php?m={$prem}'><</a> ";
echo "<div>{$mon}月</div> ";
echo "<a href='sy1.php?m={$nextm}'>></a>";
echo "</td></tr>";