Question

nodejs版本v10.14.2 操作系统win7 sp1 64位

我需要以下四行代码才能按顺序执行

var res2 = await fetchData(url_2, file_path_2);
await console.log('step one.');
var res1 = await fetchData(url_1, file_path_1);
await console.log('step two.');

但是，其执行的实际顺序是

第一步。第二步。 ........ ........

我们如何实现这四行代码的同步执行？

var https = require('https');
var fs = require('fs');
var request = require('request');
var async = require("async");

(async() => {

var url_1 = 'https://aaa.bbb.ccc.com';
var url_2 = 'https://library.harvard.edu/';

var file_path_1 = fs.createWriteStream('./intelcenter/aaa.bbb.ccc.txt');
var file_path_2 = fs.createWriteStream('./intelcenter/harvard.txt');

var res2 = await fetchData(url_2, file_path_2);
await console.log('step one.');
var res1 = await fetchData(url_1, file_path_1);
await console.log('step two.');

})();


async function fetchData(url,locpath) {
  return new Promise(function (resolve) {
    async.retry(request(url).pipe(locpath), function(err, result) {
    resolve(result);
    });   
 });
}

Answer 1

同步代码

我为请求模块添加了回调函数，并通过下一个方法传递结果。

默认情况下，async.retry将重试5次。

var fs = require("fs");
var request = require("request");
var async = require("async");

(async () => {
  var url_1 = "https://google.com";
  var url_2 = "https://library.harvard.edu/";

  var file_path_1 = fs.createWriteStream("./intelcenter/aaa.bbb.ccc.txt");
  var file_path_2 = fs.createWriteStream("./intelcenter/harvard.txt");

  var res2 = await fetchData(url_2, file_path_2);
  console.log("step one." + res2);
  var res1 = await fetchData(url_1, file_path_1);
  console.log("step two." + res1);
})();

function fetchData(url, locpath) {
  console.log("inside fetchData");
  return new Promise(function(resolve, reject) {
    async.retry(
      function(next) {
        request(url, function(err, result) {
          if (err) {
            console.log(err);
          }
          console.log("inside request");
          next(result);
        }).pipe(locpath);
      },
      function(result) {
        resolve(result);
      }
    );
  });
}

进一步了解async。

没有async.retry的同步代码

var fs = require("fs");
var request = require("request");

(async () => {
  var url_1 = "https://google.com";
  var url_2 = "https://library.harvard.edu/";

  var file_path_1 = fs.createWriteStream("./intelcenter/aaa.bbb.ccc.txt");
  var file_path_2 = fs.createWriteStream("./intelcenter/harvard.txt");

  var res2 = await fetchData(url_2, file_path_2);
  console.log("step one.");
  var res1 = await fetchData(url_1, file_path_1);
  console.log("step two.");
})();

function fetchData(url, locpath) {
  console.log("inside fetchData");
  return new Promise(function(resolve, reject) {
    request(url, function(err, result) {
      if (err) {
        console.log(err);
      }
      console.log("got result");
      result=JSON.stringify(result);
      locpath.write(result);
      resolve(result);
    });
  });
}

Node.js中带有async.retry的同步请求

1 个答案: