如何使用 Promises 在 Node 中编写同步函数

Question

1.How 在 Node 中同步编写 Promise，这样我就可以获得我想要的输出。我是新手，非常感谢任何 help/suggestion.

// This is my core function

 var compareData = function(userIdArray) {
  return new Promise(function(resolve, reject) {
    var missingArray = new Array();
    userIdArray.forEach(function(id) {
      var options = {
        method: 'POST',
        url: 'http://localhost:6006/test1',
        headers:{
         'content-type': 'application/json' },
          body: { email: id },
          json: true
        };

      request(options, function (error, response, body) {
        missingArray.push(body);
      });
    });
    resolve(missingArray);
  });
}


//I'm calling my function here

compareData(userIdArray)
.then(function(missingArray){
  console.log("The Body is: "+ missingArray);
});

/* I expect the console.log to print the missingArray with data from my POST call, 
but it prints an empty array. Can someone please tell me how to do this synchronously.
I'm pretty new to Node and finding it difficult to understand.*/

Answer 1

与 bluebird and request-promise:

var Promise = require('bluebird');
var request = require('request-promise');

var compareData = function(userIdArray) {
    //Promise.all(): 
        //takes an array of promises (and/or values), 
        //returns a promise of the resolved array
    return Promise.all( 
        userIdArray.map(function(id){
            return request({
                method: 'POST',
                url: 'http://localhost:6006/test1',
                headers: { 'content-type': 'application/json' },
                body: { email: id },
                json: true
            });
        }) 
    );
}

有什么需要进一步解释的吗？

Answer 2

没有库，并且假设 request 还没有 return 承诺

var compareData = function(userIdArray) {
    return Promise.all(
        userIdArray.map(function(id) {
            var options = {
                method  : 'POST',
                url     : 'http://localhost:6006/test1',
                headers : { 'content-type': 'application/json' },
                body    : { email: id },
                json    : true
            };

            return new Promise(function(resolve, reject) {
                request(options, function(error, response, body) {
                    if (error) {
                        reject();
                    } else {
                        resolve(body);
                    }
                });
            });
        })
    );
}

compareData(userIdArray).then(function(missingArray) {
    console.log(missingArray);
});

Answer 3

如果您不想按照@Thomas 的回答使用外部库，您可以直接使用本机 Promises - 而且它不会太冗长

var compareData = function compareData(userIdArray) {
    return Promise.all(userIdArray.map(function (id) {
        return new Promise(function (resolve, reject) {
            var options = {
                method: 'POST',
                url: 'http://localhost:6006/test1',
                headers: {
                    'content-type': 'application/json'
                },
                body: {
                    email: id
                },
                json: true
            };
            return request(options, function (error, response, body) {
                error ? reject(error) : resolve(body);
            });
        });
    }));
};

compareData(userIdArray)
.then(function (missingArray) {
    console.log("The Body is: " + missingArray);
});

或者，因为这是节点，它可以处理更现代的代码：

var compareData = userIdArray => 
    Promise.all(userIdArray.map(id => 
        new Promise((resolve, reject) =>
            request({
                method: 'POST',
                url: 'http://localhost:6006/test1',
                headers: {
                    'content-type': 'application/json'
                },
                body: {
                    email: id
                },
                json: true
            }, (error, response, body) => error ? reject(error) : resolve(body))
        )
    ));

compareData(userIdArray)
.then(missingArray => 
    console.log("The Body is: "+ missingArray)
);

如何使用 Promises 在 Node 中编写同步函数

How to write a Synchronous function in Node using Promises

javascript

node.js

promise

synchronous