NodeJS异步/非阻塞io basic

Question

试图理解一种简单的nodejs异步方式来处理i/o，并以下面的简单代码片段为例，这给我留下了疑问。

    // Just to simulate an io (webservice call).
    var performRiskCheckViaWebservice = function(personPassportNumber, callback) {
        console.log("Risk check called for personPassportNumber: "+personPassportNumber);
        setTimeout(callback(personPassportNumber, "OK"), 5000);
    }

    function assessRisk(passportNumber) {
        performRiskCheckViaWebservice(passportNumber, function(passportNumber, status){
            console.log("Risk status of "+passportNumber+" is: "+status);
        })
    }

    assessRisk("1");
    assessRisk("2");
    assessRisk("3");

在上面的简单代码片段中，我希望看到：

Risk check called for personPassportNumber: 1
Risk check called for personPassportNumber: 2
Risk check called for personPassportNumber: 3

And 5 seconds later:
Risk status of 1 is: OK
Risk status of 2 is: OK
Risk status of 3 is: OK

但实际输出是：

Risk check called for personPassportNumber: 1
Risk status of 1 is: OK
Risk check called for personPassportNumber: 2
Risk status of 2 is: OK
Risk check called for personPassportNumber: 3
Risk status of 3 is: OK

5秒后，程序停止。

我的理解有什么问题吗？

Answer 1

结果，我不得不在setTimeout(...)中用一个匿名函数包装回调函数。以下是工作版本：

    // Just to simulate an io (webservice call).
    var performRiskCheckViaWebservice = function(personPassportNumber, callback) {
        console.log("Risk check called for personPassportNumber: "+personPassportNumber);
        setTimeout(function() {
            callback(personPassportNumber, "OK")
        }, 5000);
    }

    function assessRisk(passportNumber) {
        performRiskCheckViaWebservice(passportNumber, function(personPassportNumber, status){
            console.log("Risk status of "+personPassportNumber+" is: "+status);
        })
    }

    assessRisk("1");
    assessRisk("2");
    assessRisk("3");

Answer 2

以下是代码的同步瀑布：

sync assessRisk
sync performRiskCheckViaWebservice
sync console.log Risk.check
sync callback <== problem here
sync console.log Risk status
sync setTimeout 5000

所以你观察到的是正常的。

你可以替换

setTimeout(callback(personPassportNumber, "OK"), 5000);

通过

setTimeout(callback.bind(null, personPassportNumber, "OK"), 5000);