ECMAScript 6 链接承诺

Question

我正在尝试链接 promise，但第二个没有调用 resolve 函数。我做错了什么？

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“订单 123”：

获取客户链接的 getCustomers 和 getOrders。等待结果获取订单

Update. 我想在 return 承诺的链式方法之间的控制台上插入打印。我想这样的事情是不可能的：

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

您想链接一个成功处理程序（对于您的 resolve 结果 "Order 123"），而不是错误处理程序。所以使用 then 而不是 catch :-)

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

None 的 promise 被拒绝，因此您的代码中的 console.log(err) 从未被调用。

I wanted to insert the print on the console between chained methods that return promises. I guess something like this is not possible:
getCustomers()
  .then((cust) => console.log(cust))  //Can't print between chained promises?
  .then((cust) => getOrders(cust))

是的，这是可能的，但你在这里拦截了一条链。所以第二个 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 - 和 console.log returns 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) => …)

或更简单

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

Answer 2

这是使用 ES6 ECMAScript 为 node.js 顺序执行的代码示例。也许有人觉得它有用。 http://es6-features.org/#PromiseUsage https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_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);
    });

ECMAScript 6 链接承诺

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