如何处理 Node.js - Puppeteer 的异步行为？

Question

所以基本上我使用 puppeteer 下载 CSV 文件，然后读取 CSV 文件，然后使用我的命名结构创建一个新文件，并将该数据存放在 Dropbox 文件夹中。对于不同的帐户，此过程会一次又一次地重复。问题是由于 node.js 的异步行为，它开始下载另一个文件并且不等待文件写入过程完成。由于这个问题，文件被存储在错误的文件夹中，因为文件夹名称也在循环中传递。我该如何解决这个问题？

     const puppeteer = require('puppeteer');
     var datetime = require('node-datetime');
     var dt = datetime.create();
     dt.offsetInDays(-2);
     var start_date = dt.format('Y-m-d');
     dt.offsetInDays(1);
     var end_date = dt.format('Y-m-d');
     dt.offsetInDays(0);
     var date =  dt.format('Y-m-d');
     var fs = require('fs'),
     path = require('path'),
     _ = require('underscore');
     var user_details = [
          {
               username : 'user1', 
               password : 'password1',
               folder_name : 'folder1'
          },
          {
               username : 'user2',
               password : 'password2',
               folder_name : 'folder2'
          },
          {
               username : 'user3',
               password : 'password3',
               folder_name : 'folder3'
          },
          {
               username : 'user4',
               password : 'password4',
               folder_name : 'folder4'

          }];


     (async () => {

          console.log(user_details.length); 
          for( var i=0; i<user_details.length; i++){               
          var username = user_details[i]['username'];
          var password = user_details[i]['password'];
          var folder_name = user_details[i]['folder_name'];
          console.log(username);
          console.log(folder_name);
          const browser = await puppeteer.launch({ headless: false});
          const page = await browser.newPage();
          await page.goto('url', {waitUntil: 'networkidle2'});
          await page.waitFor('input[name=name]');
          await page.$eval('input[name=name]', (el, _username) => el.value = _username, username);
          await page.$eval('input[name=password]', (el, _password) => el.value = _password, password);
          await page.click('input[type=submit]');
          await page.waitFor('.breadcrumb')
          await page.goto('url', {waitUntil: 'networkidle2'});
          await page.waitForSelector('.csv_toggle');
          await page.click('.action');
          await page.click('.fa-files-o');  
          await page.waitFor(10000);
          var dir = '/users/user/Downloads/';
          var files = fs.readdirSync(dir);

          // use underscore for max()
          var file_name =  _.max(files, function (f) {
               var fullpath = path.join(dir, f);

               // ctime = creation time is used
               // replace with mtime for modification time
               return fs.statSync(fullpath).ctime;
          });
          var filePath = path.join('/users/user/Downloads/',file_name);
          fs.readFile(filePath, {encoding: 'utf-8'}, function(err,data){
               if (!err) {
                    lines = data;

                    fs.writeFile("/users/user/Dropbox/Puppeteer/"+folder_name+"/data_"+folder_name+"_"+date+"_.csv", data, function(err) {
                         if(err) {

                                   console.log(err);

                         }
                              console.log("The file was saved!");
                              console.log('Closing Browser');
                              browser.close();     
                         }); 
               } else {
                    console.log('-----SOMETHING IS WRONG-----');
               }
               });
              await page.waitFor(10000); 
     }
})();

上面的代码工作得很好，因为我使用了 10 秒的延迟来完成编写过程，但这是一种 hack，当互联网连接速度慢或机器速度慢时肯定不会工作。我想要的是它应该首先等待文件完全下载，然后等待文件写入过程完成，然后为下一个用户继续循环。

Answer 1

在 fs.readFile 和 fs.writeFile 方法中也添加 await。

使用

let data = await fs.readFile(filePath, {encoding: 'utf-8'});
await fs.writeFile("/users/user/Dropbox/Puppeteer/"+folder_name+"/data_"+folder_name+"_"+date+"_.csv", data);
browser.close();

而不是

fs.readFile(filePath, { encoding: 'utf-8' }, function (err, data) {
        if (!err) {
            lines = data;

            fs.writeFile("/users/user/Dropbox/Puppeteer/" + folder_name + "/data_" + folder_name + "_" + date + "_.csv", data, function (err) {
                if (err) {

                    console.log(err);

                }
                console.log("The file was saved!");
                console.log('Closing Browser');
                browser.close();
            });
        } else {
            console.log('-----SOMETHING IS WRONG-----');
        }
    });