Wrong usage of if...else..

1. Recently, when I was writing js code to complete a function that operates the previous DOM, I mistakenly used the if..else.. control body. Why is it wrong? Take a look at my

code and you will understand:

document.getElementsByClassName('eButton')[0].onclick=function(){
   var checked=document.getElementsByClassName('checked');
     var eButton=document.getElementsByClassName('eButton')[0];
   if(checked.length==0){
    alert('请选择要编辑的联系人！');
     }else{
         if(checked.length >2){
                alert('每次编辑只能选择一条记录');
         }else{
                if(checked[0].childNodes[0].id=='check-all'){
                    var email=checked[1].parentNode.nextElementSibling.nextElementSibling.innerHTML;
                    var name=checked[1].parentNode.nextElementSibling.innerHTML;
                    document.getElementsByClassName('edit_contact_name')[0].value=name;
                    document.getElementsByClassName('edit_contact_email')[0].value=email;
                    var group=checked[1].parentNode.nextElementSibling.nextElementSibling.nextElementSibling
                    if(group.innerHTML !="default"){
                        var group_id=group.getAttribute('group_id')
                        document.getElementsByClassName('edit_contact_group_name')[0].value=id;
                    }
                    $('#edit_contact').modal();
                }else{
                    if(checked.length ==2){
                        alert('每次编辑只能选择一条记录');
                    }else{
                        var email=checked[0].parentNode.nextElementSibling.nextElementSibling.innerHTML;
                        var name=checked[0].parentNode.nextElementSibling.innerHTML;
                        document.getElementsByClassName('edit_contact_name')[0].value=name;
                        document.getElementsByClassName('edit_contact_email')[0].value=email;
                        var group=checked[0].parentNode.nextElementSibling.nextElementSibling.nextElementSibling
                        if(group.innerHTML !="default"){
                            var group_id=group.getAttribute('group_id')
                            document.getElementsByClassName('edit_contact_group_name')[0].value=id;
                        }
                        $('#edit_contact').modal();
                    }
                }
       }
   }
    };

Haha, seeing the codes I wrote, I suddenly felt that this function must be very powerful. The whole function was messed up by if..else.., and I started to think about why I used if..else

. In fact, I just considered that there are about three or four different conditions in this logic, and three or four operations need to be performed. , and only one situation can be executed at a time (go to the end of the function after execution), these are the execution flow of the program. With this process in place, I began to think about how to change the code so that it would be clear at a glance and easy to maintain. At this time, I naturally thought of the keyword "return". After using "return", I got the following code:

document.getElementsByClassName('eButton')[0].onclick=function(){
  var checked=document.getElementsByClassName('checked');
    var eButton=document.getElementsByClassName('eButton')[0];
  if(checked.length==0){
    alert('请选择要编辑的联系人！');
    return;
  }
  if(checked.length ==1){
    var email=checked[0].parentNode.nextElementSibling.nextElementSibling.innerHTML;
    var name=checked[0].parentNode.nextElementSibling.innerHTML;
    document.getElementsByClassName('edit_contact_name')[0].value=name;
    document.getElementsByClassName('edit_contact_email')[0].value=email;
    var group=checked[0].parentNode.nextElementSibling.nextElementSibling.nextElementSibling
    if(group.innerHTML !="default"){
     var group_id=group.getAttribute('group_id')
     document.getElementsByClassName('edit_contact_group_name')[0].value=id;
    }
      $('#edit_contact').modal();
      return;
  }
  if(checked.length ==2){
    if(checked[0].childNodes[0].id=='check-all'){
      var email=checked[1].parentNode.nextElementSibling.nextElementSibling.innerHTML;
      var name=checked[1].parentNode.nextElementSibling.innerHTML;
      document.getElementsByClassName('edit_contact_name')[0].value=name;
      document.getElementsByClassName('edit_contact_email')[0].value=email;
      var group=checked[1].parentNode.nextElementSibling.nextElementSibling.nextElementSibling
      if(group.innerHTML !="default"){
        var group_id=group.getAttribute('group_id')
        document.getElementsByClassName('edit_contact_group_name')[0].value=id;
      }
      $('#edit_contact').modal();
      return;
    }
    alert('每次编辑只能选择一条记录');
    return;
  }
  if(checked.length >2){
    alert('每次编辑只能选择一条记录');
  }
};

The code will be much clearer when the following conditions are listed:

1.checked.length = =0

2.checked.length ==1

3.checked.length ==2

4.checked.length > 2

Next, encapsulate the duplicate code into a function (remove duplication) and get Code:

function get_edit_modal_content(node_num,checked){
    var email=checked[node_num].parentNode.nextElementSibling.nextElementSibling.innerHTML;
    var name=checked[node_num].parentNode.nextElementSibling.innerHTML;
        var contact_id=checked[node_num].parentNode.nextElementSibling.getAttribute('contact_id')
    var regular_name=/[\u4E00-\u9FA5\uF900-\uFA2D\w]*/;
    name=regular_name.exec(name)[0];
    document.getElementsByClassName('edit_contact_id')[0].value=contact_id;
    document.getElementsByClassName('edit_contact_name')[0].value=name;
    document.getElementsByClassName('edit_contact_email')[0].value=email;
    var group=checked[node_num].parentNode.nextElementSibling.nextElementSibling.nextElementSibling
    if(group.innerHTML !="default"){
     var group_id=group.getAttribute('group_id')
     document.getElementsByClassName('edit_contact_group_name')[0].value=group_id;
   }
 }
  document.getElementsByClassName('eButton')[0].onclick=function(){
    var checked=document.getElementsByClassName('checked');
    if(checked.length==0){
      alert('请选择要编辑的联系人！');
      return;
    }
    if(checked.length==1){
      get_edit_modal_content(0,checked);
      $('#edit_contact').modal();
      return;
    }
    if(checked.length==2){
      if(checked[0].childNodes[0].id=='check-all'){
        get_edit_modal_content(1,checked);
        $('#edit_contact').modal();
        return;
      }
      alert('每次编辑只能选择一条记录');
      return;
    }
    if(checked.length >2){
      alert('每次编辑只能选择一条记录');
      return;
    }
  };