如何使用Date對象從提示中獲取月份名稱，然後計算下一個生日

Question

在我的javascript程序中，我正在計算出生年份。我創建了接受不同值的提示對話框，我正在顯示這些值，但用戶給出的月份值在第二行中顯示不正確。用戶已輸入8，並顯示10月。任何人都可以幫助我找出問題嗎？我應該如何從提示中計算出所有三個數值以計算出生年份？

代碼：

var today = new Date(); 
 

 
var monthNames = ["January", "February", "March", "April", "May", "June", 
 
    "July", "August", "September", "October", "November", "December" 
 
]; 
 

 
var birth = new Date(); 
 

 
var myMonth = prompt("What month were you born in?"); 
 
var myDay = prompt("What day were you born on?"); 
 
var myYear = prompt("What year were you born in?"); 
 

 
var days = ["Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"]; 
 
var dateLoc = document.getElementById("dateField").innerHTML = "Today is " + today; 
 

 
var birthField = document.getElementById("birthField") 
 
    .innerHTML = "I was born on " + monthNames[birth.getMonth()] + ' ' + myDay + ',' + myYear + '.' + 
 
    '(' + myMonth + '/' + myDay + '/' + myYear + ')'; 
 

 

 
var secondsBetween = (endDate.getTime() - startDate.getTime())/1000 
 
endDate = new Date(today.getFullYear() + 1, myMonth, myDay); 
 
var nextBirth = document.getElementById("nextBirth").innerHTML = "I am" + endDate + "Years old, and will turn"+ +"in" ;

<p id="dateField"> </p> 
 
<p id="birthField"> </p> 
 
<p id="nextBirth"> </p>

輸出：

Answer 1

的問題是，birth.getMonth()只是返回當前個月，爲birth被簡單地設置new Date()。因爲現在是十月份，所以你總會得到October。

相反，您正在尋找訪問用戶提供的索引monthNames[myMonth - 1]。減去1是必要的，因爲索引從零開始，而月份從一開始。要有正確的月份顯示出來，只需在下面的例子中輸入月份號碼：

var today = new Date(); 
 

 
var monthNames = ["January", "February", "March", "April", "May", "June", 
 
    "July", "August", "September", "October", "November", "December" 
 
]; 
 

 
var birth = new Date(); 
 

 
var myMonth = prompt("What month were you born in?"); 
 
var myDay = prompt("What day were you born on?"); 
 
var myYear = prompt("What year were you born in?"); 
 

 
var days = ["Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"]; 
 
var dateLoc = document.getElementById("dateField").innerHTML = "Today is " + today; 
 

 
var birthField = document.getElementById("birthField") 
 
    .innerHTML = "I was born on " + monthNames[myMonth - 1] + ' ' + myDay + ',' + myYear + '.' + 
 
    '(' + myMonth + '/' + myDay + '/' + myYear + ')';

p { 
 
    text-align: center; 
 
    font-family: monospace; 
 
    font-size: 20px; 
 
}

<p id="dateField"> </p> 
 
<p id="birthField"> </p> 
 
<p id="nextBirth"> </p>

希望這有助於！ :)

Answer 2

您有monthNames[birth.getMonth()]問題，請嘗試monthNames[myMonth - 1]代替：

var birthField = document.getElementById("birthField") 
    .innerHTML = "I was born on " + monthNames[myMonth - 1] + ' ' + myDay + ',' + myYear + '.' 
    + '(' + myMonth + '/' + myDay + '/' + myYear + ')'; 

十月是當前月份的名字，它是如此，由於birth = new Date()

你的下一個生日可以通過（myMonth - 1）獲得/ myDay /（今年+ 1）。然後計算兩個日期之間的秒數，您可以使用

var secondsBetween = (endDate.getTime() - startDate.getTime())/1000 

這意味着您必須將輸入日期轉換爲javascript日期。在你的情況（只是以下specification）這是很簡單的：

endDate = new Date(today.getFullYear() + 1, myMonth - 1, myDay);