javascript - AJAX - 带有嵌套的 promise

Question

var preadd = $.ajax({
  type: 'POST',
  url: url,
  data: {
    some data
  },
  success: function(output) {

    if (output != 12 && output != 13) {

      some code here...

      var arr = [];
      arr.push.apply(arr, val.split(","));
      arr.splice(-1, 1);
      for (var i = 0; i < arr.length; i++) {
        arr[i] = arr[i].trim();
      }
      chk dup1 is another ajax
      function outside
      var chk = chkdup1();
      console.log(chk);
      chk.then(function() {
        if (result == 13) {

          rem = confirm("Duplicate data will be removed, are you sure!");
          if (rem == false) {
            return false;
          }
          if (rem == true) {
            remdens1();
          }
        }
      });
    }
    if (output == 13) {
      rem = confirm("Duplicate data will be removed, are you sure!");
      if (rem == true) {
        remdens1();
      }
    }

    if (output == 12) {
      $('#valensdata').html("success").css('color', 'green');
    }
    return rem;
  }
});

preadd.then(function() {
  console.log(rem);
  if (rem == false) {
    return false;
  }

  fnensadd();

});

1. 即使我在 preadd 的 .then 函数中按确认中的取消，
2. 我无法获取存储在 rem 变量中的值。
3. 即使返回 false，底部的 preadd.then 函数也会执行。

任何人都可以指导我吗？

Answer 1

即使我在确认中按下取消。然后 preadd 的功能:

     Promise Preadd has no knowledge of cancel. You are returning a value false when cancel is clicked.     

我无法获取存储在 rem 变量中的值。

 Assuming rem is a local variable of success function, the variable dies when success function is completed. A bad way of coding would be creating rem in  larger scope , eg sibling of preadd

即使返回 false，底部的 preadd.then 函数也会执行。

resolveCB of preadd.then( resolveCB, rejectCB) will always be called unless an until there is some error or promise is rejected. Returning false is not same as rejecting promise.   

说完这句话后，要么用“然后”，要么用“成功”。如果你想防止 CB Hell，请始终使用 Promise。

带有 Promise 的更好的代码结构如下

var preadd = $.ajax({
   type: 'POST',
   url: url,
   data: {
     some data
  }

preadd.then(function() {
     // Success of PreAdd
          return chkdup1() 
}).then(function(){
    // Success of chkdup1
    //by some internal logic build rem
    if(rem)
    return Promise.resolve(rem )
    return Promise.reject(rem)
}).then(function(data){

     // rem was true
      fnensadd();
},function(error){
    // rem was false

 });