备份JS获取日期周数

//ISO 8601
	Date.prototype.getWeek = function() {

		var y = this.getFullYear(), m = this.getMonth() + 1, d = this.getDate(), a, b, c, s, e, f, g, n, w;

		// If month jan. or feb.
		if (m < 3) {

			a = y - 1;
			b = (a / 4 | 0) - (a / 100 | 0) + (a / 400 | 0);
			c = ((a - 1) / 4 | 0) - ((a - 1) / 100 | 0) + ((a - 1) / 400 | 0);
			s = b - c;
			e = 0;
			f = d - 1 + 31 * (m - 1);

			// If month mar. through dec.
		} else {

			a = y;
			b = (a / 4 | 0) - (a / 100 | 0) + (a / 400 | 0);
			c = ((a - 1) / 4 | 0) - ((a - 1) / 100 | 0) + ((a - 1) / 400 | 0);
			s = b - c;
			e = s + 1;
			f = d + ((153 * (m - 3) + 2) / 5 | 0) + 58 + s;

		}

		g = (a + b) % 7;
		// ISO Weekday (0 is monday, 1 is tuesday etc.)
		d = (f + g - e) % 7;
		n = f + 3 - d;

		if (n < 0)
			w = 53 - ((g - s) / 5 | 0);

		else if (n > 364 + s)
			w = 1;

		else
			w = (n / 7 | 0) + 1;

		return w;

	};