each wait until finish $.ajax , and then continue

Option 1: Switch to next element in your array in the success handler.

Option 2: Make ajax requests synchronously:

• global:

   $.ajaxSetup({ async: false });
  

• or directly in the request:

   $.ajax({
       async: false,
       type: "POST",
       url: domain+"/view_tasks/gen_tasks/",
       dataType: 'html',
       data: data,
       success: function(dt){
          $this.find('.contChildTasks').html(dt);
          childs = $this.children('.taskDesc').find('.has_child');
          if(childs.length != 0) {
              genTask(childs);
          }
       }
  });