javascript - 如何同步Node.js函数(How to synchronize Nodejs functions)

Question

I am working on a NodeJs server and I am implementing a Sqlite3 database.(我正在使用NodeJs服务器，正在实现Sqlite3数据库。)

My problem is that the "saveMddToDb" method starts before the "createMddTables" method is finished.(我的问题是“ saveMddToDb”方法在“ createMddTables”方法完成之前开始。) So I would like to know how to wait until the end of the first one before starting the second one.(所以我想知道如何等到第一个开始之后再开始第二个。) const db = require('./db.js'); const myDb = new db(configServer.dataBase.useDatabase === true ? configServer.dataBase.name : null); myDb.createMddTables(); myDb.saveMddToDb(dataModel); class Db { constructor(name) { this.db = new sqlite3.Database(name === null ? ':memory:' : name, err => { if (err) { return console.error(err.message); } console.log(colors.yellow(`Connected to the ${name === null ? 'memory' : name} SQlite database`)); }); } close() { this.db.close(err => { if (err) { return console.error(err.message); } console.log(colors.yellow('Close the database connection')); }); }; createMddTables() { this.createTableContacts(); }; createTableContacts() { const sql = `CREATE TABLE IF NOT EXISTS contacts ( id TEXT PRIMARY KEY, firstName TEXT NOT NULL, lastName TEXT NOT NULL, nickName TEXT NOT NULL, profilePicture BLOB)`; this.db.run(sql, err => { if (err) { return console.log(err.message); } console.log(colors.yellow('Table contacts created')); }); }; saveMddToDb(mddJson) { if(mddJson) { const sqlContacts = `INSERT OR IGNORE INTO contacts VALUES (?, ?, ?, ?, ?)`; mddJson.contacts.forEach(contact => { this.db.run(sqlContacts, [uuidv4(), contact.firstName, contact.lastName, contact.lastName, contact.profilePicture], err => { if (err) { return console.log(err.message); } console.log(colors.yellow('Contacts added to database')); }); }); } } }; module.exports = Db;   ask by GuillaumeF translate from so

Answer 1

You can do this by using Promises .(您可以使用Promises做到这一点。)

Also, as suggested before, you can use async/await , which is syntactic sugar for Promises, so you can write your code like synchronous code.(另外，如前所述，您可以使用async / await ，它是Promises的语法糖，因此您可以像同步代码一样编写代码。) An async/await function always returns a Promise, so before using it I'd recommend you look up Promises first, and try to write your code with them.(异步/等待功能始终返回Promise，因此在使用它之前，我建议您先查找Promises，然后尝试用它们编写代码。) As soon as that works, you can rewrite it using async/await, so you know you fully understand what you're using and why it works!(一旦可行，您就可以使用async / await重写它，因此您知道自己完全了解自己在使用什么以及它为什么起作用！)