Question

这是注释的完整代码。

//program purpose:
//list all directories in a given path.
//choose a file and print wether it's a regular file  or a directory;
fs = require('fs'); //filesystem
const readline = require('readline-sync');// reads input
var dirPath = readline.question("enter directory path.\n>>> ");
//reads directory with dirPath;
fs.readdir(dirPath,(err,files)=>{
  if (err) {
    console.log("Oopps there has been an error. ");
    console.log(err);
  }else {
    //prints files in the directory.
    for (var i = 0; i < files.length; i++) {
      console.log(i+")"+files[i]);
    }
    //choose a file.
    var filePath = readline.question("Choose a file.\n>>> ");
    //checks if the choice is a file or directory
    fs.stat(dirPath+filePath,(err,stats)=>{
      if (err) {
        console.log("Oopps there has been an error. ");
        console.log(err);
      }else {
        if (stats.isDirectory()) {
          console.log("its a directory.");
          //if its a file print its content
        }else {
          fs.readFile(dirPath+filePath,'utf-8',(err,data)=>{
            if (err) {
              console.log("Oopps there has been an error. ");
              console.log(err);
            }

            else {
              console.log(data);
            }
          })
        }
      }
    })
  }

});

我试图掌握javascript的异步特性，我想重构代码： Code2

问题：第二张图片，readir被文件路径输入打断，我该如何解决，我希望代码看起来不错，并能够递归使用这些功能。

Answer 1

ES6生成器可以消除回调地狱。并且还允许您添加程序流就像循环，我已将其添加到您的示例中以显示这是多么容易。

我还添加了相应的require()行，并制作了readline.question 到另一个异步函数中，因此它将作为一个完整的节点上的示例。

const fs = require("fs");
const readline = require("readline").createInterface({
    input: process.stdin,
    output: process.stdout
});
function* myGenerator(dirPath) {
    const callback = yield;
    const [err1, files] = yield fs.readdir(dirPath, callback);
    if (err1) {
        console.log("Oopps there has been an error. ");
        console.log(err1);
        return;
    }
    //prints files in the directory.
    for (var i = 0; i < files.length; i++) {
        console.log(i + ")" + files[i]);
    }
    //choose a file.
    var filePath;
    while (true) {
        [filePath] = yield readline.question("Choose a file.\n>>> ", callback);
        //checks if the choice is a file or directory
        console.log("aaa", dirPath, "bbb", filePath);
        const[err2, stats] = yield fs.stat(dirPath + filePath, callback);
        if (err2) {
            console.log("Oopps there has been an error. Try again.");
            console.log(err2);
        } else if (stats.isDirectory()) {
            console.log("its a directory. Try again");
        } else {
            break; // OK choice
        }
    }
    // it's a file. Print its content
    const [err3, data] = yield fs.readFile(dirPath + filePath, 'utf-8', callback);
    if (err3) {
        console.log("Oopps there has been an error. ");
        console.log(err3);
        return;
    }
    console.log(data);
}

// Create and run the generator
const gen = myGenerator("./"); // Create it
gen.next(); // Start it
gen.next((...args) => gen.next([...args])); // Set its callback function

通过比较，仅靠承诺不能让您使用循环。异步/等待方法与使用生成器的好处相似但它要求您将所有异步调用都包装在Promises中。因此，我发现生成器更容易。

Answer 2

有几种方法，使用它们可以使其变得简单。

模块化-使每个回调成为独立的函数

承诺-保留异步操作的最终结果。由于它是面向对象的，因此您将获得流畅的界面。因此，通过链接调用方法。

异步/等待-它是#: import CheckBox kivy.uix.checkbox <ColoredBackground@Image>: font_size: '48sp' color: (.9, .5, .4, 1) canvas.before: Color: rgb: (.9, .9, .9) Rectangle: pos: self.x + sp(2), self.y + sp(2) size: self.width - sp(5), self.height - sp(4) <SampBoxLayout>: orientation: "vertical" padding: 10 spacing: 10 # ---------- Button FileChooser ---------- BoxLayout: orientation: "horizontal" height: 30 Button: text: "FileChooser-1" on_press: root.get_image_one() Button: text: "FileChooser-2" on_press: root.get_image_two() # ---------- Display Images---------- BoxLayout: orientation: "horizontal" height: 30 ColoredBackground: source: " " # <----------- should be the image file selected by FileChooser-1 size: self.parent.width, self.parent.height allow_stretch: True keep_ratio: False ColoredBackground: source: " " # <----------- should be the image file selected by FileChooser-2 size: self.parent.width, self.parent.height allow_stretch: True keep_ratio: False的功能实现。它的工作方式与Promise相同。

这些无效，因为您可以使用名为async的该库

如何在这个简单的程序中避免回调地狱？

2 个答案: