Node.JS - 在执行代码之前等待函数完成

Question

我不是一个整体具有Node.JS和Javascript的专业人员，所以请原谅我，如果这是一个愚蠢的问题。

我正在运行一个Node.JS服务器来接受我将要运行的网站的套接字连接，并且这个脚本要做的一部分是联系数据库。我有一个功能，旨在在启动服务器之前执行此操作。但是，当我调用该函数时，它会继续执行代码的其余部分，并且不会等待该函数完成。我尝试过使用回调但无济于事，我不知道如何使用Promise。有人可以解释我如何解决这个问题？

这里是我的参考代码：

function GetCompetitionInfo(competitionID,callback){ 
    var competitionInfo = { 
     id:competitionID, 
     title:"", 
     topic:"", 
     difficulty:"", 
     description:"", 
     jackpot:0, 
     answer:0, 
     author:0 
    } 
    var testVariable; 
    sqlConnection_read.connect(function(err){ 
     if(err) throw err; 
     console.log("Connected to TSDB, retrieving competition info..."); 
     var query = "SELECT * FROM competitions WHERE PuzzleID="+competitionID+";"; 
     sqlConnection_read.query(query,function(err,result){ 
      if(err) {console.log("Uh oh spaghettiohs");throw err;} 
      competitionInfo.title = result[0].Puzzle_Title; 
      competitionInfo.topic = result[0].Puzzle_Topic; 
      competitionInfo.difficulty = result[0].Puzzle_Difficulty; 
      competitionInfo.description=result[0].puzzle_description; 
      competitionInfo.answer=result[0].Puzzle_Answer; 
      competitionInfo.jackpot=result[0].Puzzle_Jackpot; 
      competitionInfo.author=result[0].Puzzle_Author; 
      callback(competitionInfo); 
     }); 
    }); 
} 
GetCompetitionInfo(0,function(data){ 
    competitionInfo=data;//This is a variable outside of the scope 
}); 
//I want this to be executed afterwards 
var competitionTitle = competitionInfo.title; 
var competitionTopic = competitionInfo.topic; 
var competitionDifficulty = competitionInfo.difficulty; 
var competitionDescription = competitionInfo.description; 
var competitionAnswer = competitionInfo.answer; 
var jackPotTotal = competitionInfo.jackpot; 
var competitionAuthor = competitionInfo.author; 

console.log("Title:"+competitionTitle); 
console.log("Topic:"+competitionTopic); 
console.log("Difficulty:"+competitionDifficulty); 
console.log("Description:"+competitionDescription); 
console.log("Answer:"+competitionAnswer); 
console.log("Jackpot:"+jackPotTotal); 
console.log("Author UID:"+competitionAuthor); 

但这似乎GetCompetitionDetails功能完成之前立即执行。我如何让它们一个接一个执行？

Answer 1

NodeJS和JavaScript利用callbacks来控制应用程序的流程。 Promises简化了代码，因此您不会在callback hell之类的事情中结束。

最简单的解决这个问题，以你的任务进入回调：

// function(data) { ... } is the callback that will be executed AFTER GetCompetitionInfo is finished. Anything you want to do after will have to be in that function. 
GetCompetitionInfo(0, function(data){ 

    // everything in this block will be run AFTER GetCompetitionInfo is finished 
    competitionInfo=data; 

    var competitionTitle = competitionInfo.title; 
    var competitionTopic = competitionInfo.topic; 
    var competitionDifficulty = competitionInfo.difficulty; 
    var competitionDescription = competitionInfo.description; 
    var competitionAnswer = competitionInfo.answer; 
    var jackPotTotal = competitionInfo.jackpot; 
    var competitionAuthor = competitionInfo.author; 

    console.log("Title:"+competitionTitle); 
    console.log("Topic:"+competitionTopic); 
    console.log("Difficulty:"+competitionDifficulty); 
    console.log("Description:"+competitionDescription); 
    console.log("Answer:"+competitionAnswer); 
    console.log("Jackpot:"+jackPotTotal); 
    console.log("Author UID:"+competitionAuthor); 

}); 

有关这一切的详细信息检查答案中重复的问题：How do I return the response from an asynchronous call?