javascript - NodeJS : Don't wait for function return

Question

我目前正在从 NodeJS 开始，我想使用不同的参数多次运行相同的函数，但我不确定如何运行。根据我目前的经验，NodeJS/JavaScript 一般不会等待函数返回，但就我而言，它确实会等待，这让我很困惑。

我当前的代码如下所示:

XMLHttpRequest = require("xmlhttprequest").XMLHttpRequest;
start=function(values){
    max=5
    started=0
    finished=0
    maxReachedBefore=false
    finishedStarting=false
    result=[]
    
    interval = setInterval(function(){
        if(!finishedStarting){
            if((started-finished)>= max) {
                if(!maxReachedBefore){
                    console.log("Max Reached!")
                    maxReachedBefore=true
                }
                return;
            }
            maxReachedBefore=false
            getValue(values[started])
            console.log("Started getValue")
            started++
        } else {
            if (started<=finished){
                clearInterval(interval)
                console.log("Finished!")
            }
        }
        
    },10)
}

getValue=function(value){
    var request=new XMLHttpRequest()
    request.open("get","MY_WEBSITE_HERE.COM/"+value, false)
    request.send()
    result=result.concat(request.responseText)
    console.log("Finished getValue")
    finished++
}

start(["a","medium","sized","list","of","values","that","i","want","to","get","the","corresponding","values","to"])

现在我希望在未达到最大值时继续以不同的值启动 getValue -> getValue 运行次数少于 6 次，但事实并非如此。 getValue 是逐一开始的，只有在上一个完成后才开始下一个。

有人可以解释为什么会发生这种情况/帮我改变它吗？

请怜悯，我对 NodeJS 还比较陌生

Answer 1

您正在向服务器发送同步请求。因此该函数将等待服务器的响应。

request.open("get","MY_WEBSITE_HERE.COM/"+value, false)

最后一个参数boolean指定调用是同步还是异步。

request.open("get","MY_WEBSITE_HERE.COM/"+value, true)

这将发送异步调用，并在回调函数中添加完成获取值的控制台语句。

var finished = 0;
var result=[];
 start=function(values){
 max=5
 started=0    
 maxReachedBefore=false
 finishedStarting=false

  interval = setInterval(function(){
    if(!finishedStarting){
        if((started-finished)>= max) {
            if(!maxReachedBefore){
                console.log("Max Reached!")
                maxReachedBefore=true; 
                finishedStarting = true;
            }
            return;
        }
        maxReachedBefore=false; 
        console.log("Started getValue " + values[started]);

        getValue(values[started]); 
        started++;

    } else {
        if (started<=finished){
            clearInterval(interval)
            console.log("Finished!")
        }
    }

  },10);
}

getValue=function(value){
    var request=new XMLHttpRequest()
    request.open("get","MY_WEBSITE_HERE.COM/"+value, true); 

    request.onreadystatechange = function () {
     if(request.readyState === 4 && request.status === 200) {
       result=result.concat(request.responseText);
       console.log("Finished getValue " + value)
       finished++;
     }
    };
   request.send();
   console.log("request sent");
}