javascript 获得一年中的周数
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Get weeks in year
提问by basarat
Moment js has a function to get the number of days in a month : http://momentjs.com/docs/#/displaying/days-in-month/
Moment js 有一个函数可以获取一个月中的天数：http: //momentjs.com/docs/#/displaying/days-in-month/
However I could not find a function to find the number of iso weeks in a year (52 or 53).
但是我找不到一个函数来查找一年中的 iso 周数（52 或 53）。
回答by RobG
Here's an answer that isn't dependent on a library. It uses a function to calculate the week in the year that 31 December falls in for the required year. If the week is 1 (i.e. 31 December is in the first week of the following year), it moves the day number lower until it gets a different value, which will be the last week of the required year.
这是一个不依赖于图书馆的答案。它使用一个函数来计算所需年份的 12 月 31 日所在的那一周。如果周为 1（即 12 月 31 日在下一年的第一周），它会将天数向下移动，直到获得不同的值，这将是所需年份的最后一周。
function getWeekNumber(d) {
// Copy date so don't modify original
d = new Date(+d);
d.setHours(0, 0, 0, 0);
// Set to nearest Thursday: current date + 4 - current day number
// Make Sunday's day number 7
d.setDate(d.getDate() + 4 - (d.getDay() || 7));
// Get first day of year
var yearStart = new Date(d.getFullYear(), 0, 1);
// Calculate full weeks to nearest Thursday
var weekNo = Math.ceil((((d - yearStart) / 86400000) + 1) / 7)
// Return array of year and week number
return [d.getFullYear(), weekNo];
}
function weeksInYear(year) {
var month = 11,
day = 31,
week;
// Find week that 31 Dec is in. If is first week, reduce date until
// get previous week.
do {
d = new Date(year, month, day--);
week = getWeekNumber(d)[1];
} while (week == 1);
return week;
}
[2015, 2016, 2029, new Date().getFullYear()].forEach(year =>
console.log(`${year} has ${weeksInYear(year)} weeks`)
);The getWeekNumbercode is from here: Get week of year in JavaScript like in PHP.
该getWeekNumber代码是从这里：获得今年的JavaScript的一周像PHP。
Edit
编辑
Alternatively, if 31 December is in week 1 of the following year, then the subject year has 52 weeks and otherwise has 53 weeks.
或者，如果 12 月 31 日在下一年的第 1 周，则该主题年有 52 周，否则有 53 周。
function getWeekNumber(d) {
d = new Date(+d);
d.setHours(0, 0, 0, 0);
d.setDate(d.getDate() + 4 - (d.getDay() || 7));
var yearStart = new Date(d.getFullYear(), 0, 1);
var weekNo = Math.ceil((((d - yearStart) / 86400000) + 1) / 7)
return [d.getFullYear(), weekNo];
}
function weeksInYear(year) {
var d = new Date(year, 11, 31);
var week = getWeekNumber(d)[1];
return week == 1 ? 52 : week;
}
[2015, 2016, 2029, new Date().getFullYear()].forEach(year =>
console.log(`${year} has ${weeksInYear(year)} weeks`)
);回答by basarat
Use isoWeek on the last day of the year to get the number of weeks e.g. :
在一年的最后一天使用 isoWeek 来获取周数，例如：
function weeksInYear(year) {
return Math.max(
moment(new Date(year, 11, 31)).isoWeek()
, moment(new Date(year, 11, 31-7)).isoWeek()
);
}
回答by S?ren H?yer Kristensen
Feb. 4th 2014the weeksInYear & isoWeeksInYear functions were added to moment.js
2014 年 2 月 4 日，weeksInYear 和 isoWeeksInYear 函数被添加到 moment.js
So today you can just use moment().isoWeeksInYear()or moment().weeksInYear()
所以今天你可以使用moment().isoWeeksInYear()或moment().weeksInYear()
For more into see the docs
有关更多信息，请参阅文档
