Question

我正在转换用node.js编写的AWS lambda函数来使用promises而不是回调。我用处理程序代码将所有函数包装在处理程序中。我试图打破简单的函数，这样我就可以在处理程序代码中拥有尽可能平坦的promise链。

我陷入了一个点，我有一个.then（），它返回一个值，我需要传递给我的一个函数，它已经被保证，以及其他参数。我搜索过高和低低，但无法找到执行此操作的语法示例。我甚至不确定我所做的事情是对的。我发现的所有文章都解释了只通过.then（）方法返回值的简单承诺链。没有，然后将其传递给另一个宣传的功能。

这是我到目前为止所拥有的：

var bbPromise = require("./node_modules/bluebird");
var AWS = require("./node_modules/aws-promised");
var rp = require("./node_modules/request-promise");
var moment = require('./node_modules/moment.js');
var dynamodb = new AWS.dynamoDb();

exports.handler = function(event, context) { 
    "use-strict"; 

    // This gets a token that will be used as a parameter for a request
    function getToken(params){
        return rp.post({
            url: "https://api.something.com/oauth2/token",
            followRedirects: true,
            form: params,
            headers: {'Content-Type': 'application/x-www-form-urlencoded'}
        }).then(function(body){
            return JSON.parse(body).access_token;
        }).catch(function(error){
            console.log("could not get token: "+error);
        });
    }

    function getData(userId, db, token){ 
        var qParams = {
            // params that will get one record 
        };
        return dynamodb.queryPromised(qParams)
        .then(function (data){
            var start_date = // did some date manipulation on data to get this value
            // Request records, passing the token in the header
            var url = "https://api.something.com/data/?db="+db+"&start_date="+start_date;
            var headers = {
              'Content-Type': 'application/x-www-form-urlencoded',
              'Authorization':'Bearer '+token
            };
            tokenParams = {all the parameters};
            rp.get({
                url:url, 
                qs:tokenParams, 
                headers:headers, 
                followRedirect: true
            }).then(function(body){
                return body;
            }).catch(function(error){
                console.log("could not get data: "+error);
            });
        }).catch(function(error){
            console.log("Final Catch - getData failed: "+error);
        });
    }

    // THIS IS WHERE THE HANDLER CODE STARTS

    // Get an array of all userIds then get their data
    dynamodb.scanPromised({
        // params that will get the user Ids
    }).then(function(users){
        for(var i=0; i<users.length; i++){
            userId = // the value from the user record;        
            // Request a token
            var tokenParams = {an object of params};
            getToken(tokenParams)
            .then(function(token){
            ///////////// THIS IS WHERE I NEED HELP /////////////////
            /* Is there a way to pass getData the token within the .then() so I don't have a nested promise? */
                getData(userId, users[i].dbName, token)

            //////////////////////////////////////////////////////////
            }).catch(function (e){
                console.log("caught an error");
            });
        }
    }).catch(function (e){
        console.log("caught an error");
    });
};

Answer 1

您可以使用Promise.all()，.then()，Function.prototype.bind();来自return

的rp.get() getData()

 return Promise.all(users.map(function(user) {
   userId = // the value from the user record;        
     // Request a token
     var tokenParams = {
       an object of params
     };
   return getToken(tokenParams)
     .then(getData.bind(null, userId, user.dbName))
     .catch(function(e) {
       console.log("caught an error");
       throw e
     });
 }))

Answer 2

使用promise时，您的代码应该更像这样。

when.try(() => {
    return api.some_api_call
})
.then((results) => {
    const whatIAmLookingFor = {
        data: results.data
    };

    someFunction(whatIAmLookingFor);
})
.then(() => {
    return api.some_other_api_call
})
.then((results) => {
    const whatIAmLookingFor = {
        data: results.data
    };

    someOtherFunction(whatIAmLookingFor); 
.catch(() => {
    console.log('oh no!');
})
});

如何使用JavaScript承诺字符串中的.then函数调用带参数的函数？

2 个答案: