setInterval（）無法正常工作

Question

我是JavaScript新手。我運行我的代碼，根據輸入計算用戶已經存活的時間。如果您希望看到代碼運行，則可以在我的課程測試服務器上獲得，代碼爲here。

我的代碼的問題是setInterval（）不能正常工作。根據我的理解，我的html頁面應該每隔1000ms（1s）更新一次，但是它不做任何更新。

我已經使用了setInterval（）之前的一個類似的項目，顯示自Epoch以來的秒數，它工作正常。它更新了它應該的秒數。也許我的代碼中有其他東西不允許它工作？我已經通過jslint和jshint運行我的代碼，並且找不到我犯的錯誤。

在此先感謝！

function getUserBirthday(myEpoch) { 
    "use strict"; 
    var unixEpoch = new Date()/1000.0; 
    var secondSince = unixEpoch - myEpoch; 
    var leftOrAlive = ""; 
    if (secondSince < 0) { 
     leftOrAlive = ": Seconds Left"; 
     secondSince = secondSince * -1; 
    } else { 
     leftOrAlive = ": Seconds Alive"; 
    } 
    document.getElementById("secondsAlive").innerHTML = secondSince + leftOrAlive; 
    var years = secondSince/31556926; 
    secondSince = secondSince % 31556926; 
    var months = secondSince/2629743; 
    secondSince = secondSince % 2629743; 
    var days = secondSince/86400; 
    secondSince = secondSince % 86400; 
    var hours = secondSince/3600; 
    secondSince = secondSince % 3600; 
    var minutes = secondSince/60; 
    secondSince = secondSince % 60; 
    var seconds = secondSince; 
    //Convert Variables To String 
    years = years.toString(); 
    months = months.toString(); 
    days = days.toString(); 
    hours = hours.toString(); 
    minutes = minutes.toString(); 
    seconds = seconds.toString(); 
    //Remove Trailing Decimal Places 
    var yearStr = years.slice(0, (years.indexOf("."))); 
    var monthStr = months.slice(0, (months.indexOf("."))); 
    var dayStr = days.slice(0, (days.indexOf("."))); 
    var hourStr = hours.slice(0, (hours.indexOf("."))); 
    var minuteStr = minutes.slice(0, (minutes.indexOf("."))); 
    var secondStr = seconds.slice(0, (seconds.indexOf("."))); 
    //Show Results 
    document.getElementById("years").innerHTML = yearStr + ": Years"; 
    document.getElementById("months").innerHTML = monthStr + ": Months"; 
    document.getElementById("days").innerHTML = dayStr + ": Days"; 
    document.getElementById("hours").innerHTML = hourStr + ": Hours"; 
    document.getElementById("minutes").innerHTML = minuteStr + ": Minutes"; 
    document.getElementById("seconds").innerHTML = secondStr + ": Second 
} 

function updateTimeSinceEpoch() { 
    "use strict"; 
    var strDate = prompt("Enter your birthday: ex. November 12, 1996 00:00:00"); 
    document.getElementById("birthday").innerHTML = strDate; 
    var myDate = new Date(strDate); // Your timezone! 
    var myEpoch = myDate.getTime()/1000.0; 
    var runFunction = getUserBirthday(myEpoch); 
    setInterval(runFunction, 1000); 
} 

Answer 1

當你使用：

var runFunction = getUserBirthday(myEpoch); 
setInterval(runFunction, 1000); 

的runFunction變量是undefined，因爲getUserBirthday()方法不返回任何東西。所以用這個結構中的功能將只執行一次：

function getUserBirthday(message) { 
 
    console.log(message); 
 
} 
 

 
var runFunction = getUserBirthday("Hello"); 
 
setInterval(runFunction, 1000);

嘗試使用下面的結構，它應該做的伎倆：

function getUserBirthday(message) { 
 
    console.log(message); 
 
} 
 

 
setInterval(function() { 
 
    getUserBirthday('Hello'); 
 
}, 1000);