ECMAScript 6链接承诺

Question

我试图连锁承诺，但第二个不调用解决函数。我做错什么了？

function getCustomers(){

  let promise = new Promise((resolve, reject) => {
      console.log("Getting customers");
      // Emulate an async server call here
      setTimeout(() => {
        var success = true;
        if (success) {
          resolve( "John Smith"); // got the customer
        } else {
          reject("Can't get customers");
        }
      }, 1000);

     }
  );
  return promise;
}

function getOrders(customer) {

  let promise =  new Promise((resolve, reject) => {
      console.log("Getting orders");
      // Emulate an async server call here
      setTimeout(() => {
        var success = true;
        if (success) {
          resolve("Order 123"); // got the order
        } else {
          reject("Can't get orders");
        }
      }, 1000);

     }
  );
  return promise;
}

getCustomers()
  .then((cust) => getOrders(cust))
  .catch((err) => console.log(err));

console.log("Chained getCustomers and getOrders. Waiting for results");

代码从第二个函数打印“获取订单”，但不打印"Order 123"：

让客户把getCustomers和getOrders联系在一起。等待收到订单的结果

Update. I希望在返回承诺的链式方法之间插入控制台上的打印。我想这种事是不可能的：

getCustomers()
  .then((cust) => console.log(cust))  //Can't print between chained promises?
  .then((cust) => getOrders(cust))  
  .then((order) => console.log(order))
  .catch((err) => console.error(err));

Answer 1

您希望链接一个成功处理程序(对于resolve结果"Order 123")，而不是一个错误处理程序。所以使用then而不是catch :-)

getCustomers()
  .then(getOrders)
  .then((orders) => console.log(orders))
  .catch((err) => console.error(err));

所有的承诺都没有被拒绝，所以代码中的console.log(err)从未被调用。

我想在控制台上插入返回承诺的链式方法之间的打印。我想这种事是不可能的： getCustomers() .then((cust) => console.log(cust)) //不能在连锁承诺之间打印？.then((cust) => getOrders(cust))

是的，这是可能的，但你在这里拦截了一条链。因此，第二个then回调实际上不是用cust调用的，而是用第一个then回调的结果调用的-- console.log返回undefined，getOrders会遇到一些问题。

你要么做

var customers = getCustomers();
customers.then(console.log);
customers.then(getOrders).then((orders) => …)

或者更简单

getCustomers()
  .then((cust) => { console.log(cust); return cust; })
  .then(getOrders)
  .then((orders) => …)

Answer 2

下面是使用node.js的ES6 ECMAScript顺序执行的代码示例。也许有人觉得它有用。http://es6-features.org/#PromiseUsage Objects/Promise

var soapClient = easysoap.createClient(params);

//Sequential execution for node.js using ES6 ECMAScript
console.log('getAllFunctions:');
soapClient.getAllFunctions()
    .then((functionArray) => {
        return new Promise((resolve, reject) => {
            console.log(functionArray);
            console.log('getMethodParamsByName:');
            resolve();
        });
    })
    .then(() => {
        return soapClient.getMethodParamsByName('test1'); //will return promise
    })
    .then((methodParams) => {
        console.log(methodParams.request); //Console log can be outside Promise like here too
        console.log(methodParams.response);
        console.log('call');

        return soapClient.call({ //Return promise
            method: 'test1',
            params: {
                myArg1: 'aa',
                myArg2: 'bb'

            }
        });
    })
    .then((callResponse) => {
        console.log(callResponse);  // response data as json
        console.log('end');
    })
    .catch((err) => {
        throw new Error(err);
    });