Node.JS - 在執行代碼之前等待函數完成

Question

我不是一個整體具有Node.JS和Javascript的專業人員，所以請原諒我，如果這是一個愚蠢的問題。

我正在運行一個Node.JS服務器來接受我將要運行的網站的套接字連接，並且這個腳本要做的一部分是聯繫數據庫。我有一個功能，旨在在啓動服務器之前執行此操作。但是，當我調用該函數時，它會繼續執行代碼的其餘部分，並且不會等待該函數完成。我嘗試過使用回調但無濟於事，我不知道如何使用Promise。有人可以解釋我如何解決這個問題？

這裏是我的參考代碼：

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); 

但這似乎GetCompetitionDetails功能完成之前立即執行。我如何讓它們一個接一個執行？

Answer 1

NodeJS和JavaScript利用callbacks來控制應用程序的流程。 Promises簡化了代碼，因此您不會在callback hell之類的事情中結束。

最簡單的解決這個問題，以你的任務進入回調：

// 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); 

}); 

有關這一切的詳細信息檢查答案中重複的問題：How do I return the response from an asynchronous call?