我的 function 的第二部分无法正常工作，但运行时没有显示错误

Question

function dropAndRetract1(e) {
  if(e.type = 'mouseover') {
    ul.eq(0).slideDown(1000).show();
  } else if(e.type = 'mouseout') {
    ul.eq(0).slideUp(1000).hide();
  }
}

th.eq(0).on('mouseover mouseout', dropAndRetract1);

Answer 1

function dropAndRetract1(e) {
  if(e.type == 'mouseover') {
    ul.eq(0).slideDown(1000).show();
  } else if(e.type == 'mouseout') {
    ul.eq(0).slideUp(1000).hide();
  }
}

th.eq(0).on('mouseover mouseout', dropAndRetract1);

Error is not shown because you are assigning the value instead of comparing in if condition. Use "==" or "===" for comparison.