Javascript:计算从出生年份到今天的天数、小时、分钟、秒

在我的程序中，通过提示值计算出生年份、下一个轮回年份、天、小时、分钟和秒。现在我想计算一下这个人从出生日期起已经活了多久。为此，我做了以下的计算，但我的计算多少天，小时，分钟，秒的生存时间是不正确的。有人能帮忙吗？

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代码语言：javascript运行复制var monthNames = ["January", "February", "March", "April", "May", "June",

"July", "August", "September", "October", "November", "December"

];

var days = ["Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"];

var today = 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 birthday = new Date(myYear, myMonth, myDay);

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 + ')';

var milliseconds, seconds, minutes, hours, days;

var years = today.getFullYear() - birthday.getFullYear();

myMonth--;

var nextBirthday = (new Date(today.getFullYear(), myMonth, myDay)) < today ? (new Date(today.getFullYear() + 1, myMonth, myDay)) : (new Date(today.getFullYear(), myMonth, myDay))

console.log(nextBirthday);

milliseconds = diff % 1000;

diff = (diff - (milliseconds)) / 1000;

seconds = diff % 60

diff = (diff - seconds) / 60;

minutes = diff % 60

diff = (diff - minutes) / 60;

hours = diff % 24

days = (diff - hours) / 24;

var nextBirth = document.getElementById("nextBirth").innerHTML = "I am " + years + " Years old, and will turn " + (years + 1) + " in:" + "
" + days + " days, " + hours + " hours, " + minutes + " minutes, " + seconds + " seconds";

milliseconds = diffAlive % 1000;

diffAlive = (diffAlive - (milliseconds)) / 1000;

seconds = diffAlive % 60

diffAlive = (diffAlive - seconds) / 60;

minutes = diffAlive % 60

diffAlive = (diffAlive - minutes) / 60;

hours = diffAlive % 24

days = (diffAlive - hours) / 24;

var aliveFor = document.getElementById("aliveFor").innerHTML = "I have been alive for..." + "
" + days + " days, " + hours + " hours, " + minutes + " minutes, " + seconds + " seconds";代码语言：javascript运行复制p {

text-align: center;

font-family: monospace;

font-size: 20px;

}

body {

background-image: url(birth.jpg");

background-repeat: no-repeat;

background-size: 1300px 600px;

}代码语言：javascript运行复制

产出：

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