我有一段文字，上面有日期和下个月等。但在12月，我记不起1月了。
<body onload="displayDates()">
<!--dropdown ville-->
<div class="dd">
<h3 style="font-family: 'Open Sans', sans-serif;font-size:1.1em;color:#54595f; font-weight:400;">For EACH friend who signs up until <span id="currentMonth"></span> <span id="lastThursday"></span>, you’ll get a FLEX PASS which will allow you to enjoy unlimited trips with the first the 30 minutes free for a whole month, starting on <span id="nextMonth"></span> 1.</h3>
<h3 style="font-family: 'Open Sans', sans-serif;font-size:1.1em;color:#54595f; font-weight:400;">Get a second FLEX PASS starting <span id="inTwoMonths"></span> 1 if you refer a second friend and so on if you refer more friends. The more friends who sign up, the more FLEX PASSES you’ll receive!</h3>
</div>
<div id="demo"></div>
</body>
<script>
//Declare variables
var month;
var year;
var numberOfDays;
//Dynamic text to be replaced
var currentMonthText = document.getElementById("currentMonth");
var lastThursdayText = document.getElementById("lastThursday");
var nextMonthText = document.getElementById("nextMonth");
var inTwoMonthsText = document.getElementById("inTwoMonths");
//Weekdays and months
var weekdays = [ "Sun", "Mon", "Tue", "Wed", "Thurs", "Fri", "Sat" ];
var monthsName = ["January", "February", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December"];
//How many days are in this month
//1. Get the current month
function daysInMonth (month, year) {
return new Date(year, month, 0).getDate();
}
function displayDates() {
var date = new Date();
//Today's date number
var stringDate = date.toString();
var todayDate = stringDate.slice(8,10);
//console.log(stringDate);
var lastThursday;
var nextLastThursday;
month = date.getMonth() + 1;
year = date.getFullYear() ;
numberOfDays = daysInMonth(month, year);
//Find the last thursday of current month
for (var i = 1 ; i < numberOfDays ; i++) {
//Create a new date
var newDate = new Date(year,month - 1,i,0,0,0,0);
//console.log("newDate " + newDate);
var newDay = newDate.getDay();
//console.log("newDay " + newDay);
if (newDay == 4) {
//console.log(newDate);
var string = newDate.toString();
lastThursday = string.slice(8,10);
}
}
//Display info dynamically
currentMonthText.innerHTML = monthsName[month - 1];
lastThursdayText.innerHTML = lastThursday;
nextMonthText.innerHTML = monthsName[month];
inTwoMonthsText.innerHTML = monthsName[month + 1]
//Check if date to register has passed, if so show next month
var pastDate = parseInt(lastThursday);
var nextDate = parseInt(todayDate);
if (pastDate < nextDate) {
console.log("past date");
//Find the last thursday of current month
for (var i = 1 ; i < numberOfDays ; i++) {
//Create a new date
var newDate = new Date(year,month,i,0,0,0,0);
//console.log("newDate " + newDate);
var newDay = newDate.getDay();
//console.log("newDay " + newDay);
if (newDay == 4) {
//console.log(newDate);
var string = newDate.toString();
nextLastThursday = string.slice(8,10);
}
}
//Display info dynamically
currentMonthText.innerHTML = monthsName[month];
lastThursdayText.innerHTML = nextLastThursday;
nextMonthText.innerHTML = monthsName[month + 1];
inTwoMonthsText.innerHTML = monthsName[month + 2]
}
}
</script>
Pilchard的注释有你的答案(你超过了monthsName数组的长度，所以使用month = (date.getMonth()%monthsName.length)(，所以这实际上只是一个长注释。希望代码中的注释能够解释发生了什么。
如果您使用带有选项(例如{month: 'long'}(的toLocaleString来格式化日期，并使用短函数来添加日期和月份，那么代码可能会简单得多。
function updateDates() {
let d = new Date();
// Get end of month
let eom = new Date(d.getFullYear(), d.getMonth()+1, 0);
// Get last Thursday in month
let lastThuInMonth = new Date(eom);
lastThuInMonth.setDate(eom.getDate() - ((eom.getDay() - 4 + 7)%7));
// Get next and following months
let nextMonth = new Date(d.getFullYear(), d.getMonth()+1, 1);
let nextMonth2 = new Date(d.getFullYear(), d.getMonth()+2, 1);
// Simple functions to format dates as required
let getMonthStart = d => d.toLocaleString('default', {day: 'numeric', month: 'long'});
let dateTimestamp = d => d.toLocaleString('default', {day: 'numeric', weekday:'short', month: 'short'});
// Update document
document.getElementById('lastThursday').textContent = dateTimestamp(lastThuInMonth);
document.getElementById('nextMonth').textContent = getMonthStart(nextMonth);
document.getElementById('inTwoMonths').textContent = getMonthStart(nextMonth2);
}
window.onload = updateDates;<h3 style="font-family: 'Open Sans', sans-serif;font-size:1.1em;color:#54595f; font-weight:400;">For EACH friend who signs up until <span id="lastThursday"></span>, you’ll get a FLEX PASS which will allow you to enjoy unlimited trips with the first the 30 minutes free for a whole month, starting on <span id="nextMonth"></span>.</h3>
<h3 style="font-family: 'Open Sans', sans-serif;font-size:1.1em;color:#54595f; font-weight:400;">Get a second FLEX PASS starting <span id="inTwoMonths"></span> if you refer a second friend and so on if you refer more friends. The more friends who sign up, the more FLEX PASSES you’ll receive!</h3>