hyperform
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Capture form validation back from the browser
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JavaScript
;
/* For a given date, get the ISO week number
*
* Source: http://stackoverflow.com/a/6117889/113195
*
* Based on information at:
*
* http://www.merlyn.demon.co.uk/weekcalc.htm#WNR
*
* Algorithm is to find nearest thursday, it's year
* is the year of the week number. Then get weeks
* between that date and the first day of that year.
*
* Note that dates in one year can be weeks of previous
* or next year, overlap is up to 3 days.
*
* e.g. 2014/12/29 is Monday in week 1 of 2015
* 2012/1/1 is Sunday in week 52 of 2011
*/
export default function(d) {
/* Copy date so don't modify original */
d = new Date(+d);
d.setUTCHours(0, 0, 0);
/* Set to nearest Thursday: current date + 4 - current day number
* Make Sunday's day number 7 */
d.setUTCDate(d.getUTCDate() + 4 - (d.getUTCDay()||7));
/* Get first day of year */
const yearStart = new Date(d.getUTCFullYear(),0,1);
/* Calculate full weeks to nearest Thursday */
const weekNo = Math.ceil(( ( (d - yearStart) / 86400000) + 1)/7);
/* Return array of year and week number */
return [d.getUTCFullYear(), weekNo];
}