AngularJS : Seqential Promise chain

本文关键字：chain Promise Seqential AngularJS 更新时间：2023-09-26

函数one将值传递给two，然后two将值传递到three。这些函数中的任何一个都可能需要花费任何时间来返回数据。我如何让他们等待价值，而不是匆匆忙忙地打印undefined。

var deferred = $q.defer();
var one = function (msg) {
  $timeout(function () {
    console.log(msg);
    return "pass this to two";
  }, 2000);
};
var two = function (msg) {
  console.log(msg);
  return "pass this to three";
};
var three = function (msg) {
  console.log(msg);
};
deferred.promise
  .then(one)
  .then(two)
  .then(three);
deferred.resolve("pass this to one");

您需要return从每个执行异步操作的函数中获得一个promise。

在您的情况下，one函数返回undefined，而它需要在超时后返回您为"pass this to two"值创建的promise：

function one (msg) {
  return $timeout(function () {
//^^^^^^
    console.log(msg);
    return "pass this to two";
  }, 2000);
}

顺便说一句，与其使用var deferred = $q.defer();，不如将该链写成：

one("pass this to one")
  .then(two)
  .then(three);