Node.js 无法在类中使用类外变量

我正在制作一个简单的笔记应用程序来学习node和ES6。我有3个模块-应用程序、NotesManager和Note。我正在将Note类导入NotesManager，并尝试在其addNote函数中实例化它。问题是，即使导入是正确的，但在类定义中却没有定义。一个更简单的解决方案是实例化NotesManager类并将Note类添加到其构造函数中。然而，我希望将NotesManager作为静态实用程序类

这是我的密码。 Note.js

class Note {
  constructor(title, body) {
    this.title = title;
    this.body = body;
  }
}

module.exports = Note;

const note = require("./Note");
console.log("Note: ", note); //shows correctly

class NotesManager {
  constructor() {}

  static addNote(title, body) {
    const note = new note(title, body); //Fails here as note is undefined
    NotesManager.notes.push(note); 
  }

  static getNote(title) {
    if (title) {
      console.log(`Getting Note: ${title}`);
    } else {
      console.log("Please provide a legit title");
    }
  }

  static removeNote(title) {
    if (title) {
      console.log(`Removing Note: ${title}`);
    } else {
      console.log("Please provide a legit title");
    }
  }

  static getAll() {
    //console.log("Getting all notes ", NotesManager.notes, note);
  }
}

NotesManager.notes = []; //Want notes to be a static variable

module.exports.NotesManager = NotesManager;

console.log("Starting App");
const fs = require("fs"),
  _ = require("lodash"),
  yargs = require("yargs"),
  { NotesManager } = require("./NotesManager");

console.log(NotesManager.getAll()); //works
const command = process.argv[2],
  argv = yargs.argv;
console.log(argv);
switch (command) {
  case "add":
    const title = argv.title || "No title given";
    const body = argv.body || "";
    NotesManager.addNote(title, body); //Fails here
    break;
  case "list":
    NotesManager.getAll();
    break;
  case "remove":
    NotesManager.removeNote(argv.title);
    break;
  case "read":
    NotesManager.getNote(argv.title);
    break;
  default:
    notes.getAll();
    break;
}

NotesManager.js

class Note {
  constructor(title, body) {
    this.title = title;
    this.body = body;
  }
}

module.exports = Note;

const note = require("./Note");
console.log("Note: ", note); //shows correctly

class NotesManager {
  constructor() {}

  static addNote(title, body) {
    const note = new note(title, body); //Fails here as note is undefined
    NotesManager.notes.push(note); 
  }

  static getNote(title) {
    if (title) {
      console.log(`Getting Note: ${title}`);
    } else {
      console.log("Please provide a legit title");
    }
  }

  static removeNote(title) {
    if (title) {
      console.log(`Removing Note: ${title}`);
    } else {
      console.log("Please provide a legit title");
    }
  }

  static getAll() {
    //console.log("Getting all notes ", NotesManager.notes, note);
  }
}

NotesManager.notes = []; //Want notes to be a static variable

module.exports.NotesManager = NotesManager;

console.log("Starting App");
const fs = require("fs"),
  _ = require("lodash"),
  yargs = require("yargs"),
  { NotesManager } = require("./NotesManager");

console.log(NotesManager.getAll()); //works
const command = process.argv[2],
  argv = yargs.argv;
console.log(argv);
switch (command) {
  case "add":
    const title = argv.title || "No title given";
    const body = argv.body || "";
    NotesManager.addNote(title, body); //Fails here
    break;
  case "list":
    NotesManager.getAll();
    break;
  case "remove":
    NotesManager.removeNote(argv.title);
    break;
  case "read":
    NotesManager.getNote(argv.title);
    break;
  default:
    notes.getAll();
    break;
}

App.js

class Note {
  constructor(title, body) {
    this.title = title;
    this.body = body;
  }
}

module.exports = Note;

const note = require("./Note");
console.log("Note: ", note); //shows correctly

class NotesManager {
  constructor() {}

  static addNote(title, body) {
    const note = new note(title, body); //Fails here as note is undefined
    NotesManager.notes.push(note); 
  }

  static getNote(title) {
    if (title) {
      console.log(`Getting Note: ${title}`);
    } else {
      console.log("Please provide a legit title");
    }
  }

  static removeNote(title) {
    if (title) {
      console.log(`Removing Note: ${title}`);
    } else {
      console.log("Please provide a legit title");
    }
  }

  static getAll() {
    //console.log("Getting all notes ", NotesManager.notes, note);
  }
}

NotesManager.notes = []; //Want notes to be a static variable

module.exports.NotesManager = NotesManager;

console.log("Starting App");
const fs = require("fs"),
  _ = require("lodash"),
  yargs = require("yargs"),
  { NotesManager } = require("./NotesManager");

console.log(NotesManager.getAll()); //works
const command = process.argv[2],
  argv = yargs.argv;
console.log(argv);
switch (command) {
  case "add":
    const title = argv.title || "No title given";
    const body = argv.body || "";
    NotesManager.addNote(title, body); //Fails here
    break;
  case "list":
    NotesManager.getAll();
    break;
  case "remove":
    NotesManager.removeNote(argv.title);
    break;
  case "read":
    NotesManager.getNote(argv.title);
    break;
  default:
    notes.getAll();
    break;
}

我是否可以创建一个严格的实用程序类，而不用像Java那样实例化它？这里很新，我尝试过在没有任何运气的情况下搜索它。感谢您的帮助。

执行此操作时：

const note = new note(title, body);

您可以重新定义

note

从外部范围隐藏原始

note

。您需要选择一个不同的变量名

这样的方法应该更有效：

static addNote(title, body) {
    const some_note = new note(title, body); //Fails here as note is undefined
    NotesManager.notes.push(some_note); 
}

---

我实际上不知道问题是什么，但没有理由将

NotesManager

作为一个类。您可以直接从模块中导出函数。此外，有一个惯例，构造函数或类名应大写，如

Note

中所述，以直观地将其与常规函数分开。当您执行

const note=require（“./note”）时修复该问题然后更改为
const note=新注释（标题、正文）
也会解决您的问题，因为
note
实例与
note
类是分开的。我同意。这是我正在做的教程中的一个练习。他们希望以上所有内容都是课程。谢谢@jfriend00的建议。从今以后我会记住这一点，这很公平。java类实用工具类肯定是JS中的反模式，以后的注释。非常感谢快速响应。“我真不敢相信我错过了。”里夫纳特马尔萨有时你只需要一双新眼睛。