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19 lines
569 B
JavaScript
19 lines
569 B
JavaScript
function ISO8601_week_no(dt)
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{
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var tdt = new Date(dt.valueOf());
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var dayn = (dt.getDay() + 6) % 7;
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tdt.setDate(tdt.getDate() - dayn + 3);
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var firstThursday = tdt.valueOf();
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tdt.setMonth(0, 1);
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if (tdt.getDay() !== 4)
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{
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tdt.setMonth(0, 1 + ((4 - tdt.getDay()) + 7) % 7);
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}
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return 1 + Math.ceil((firstThursday - tdt) / 604800000);
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}
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dt = new Date();
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console.log(ISO8601_week_no(dt));
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dt = new Date(2015, 10, 1);
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console.log(ISO8601_week_no(dt));
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