Get date of intervals starts

getStartOfQuarter.js

    const getStartOfQuarter = date => {
        const
            quarters = {
                1: 1,
                2: 4,
                3: 7,
                4: 10
            },
            d = date ? new Date(date) : new Date(),
            q = Math.ceil((d.getMonth() + 1) / 3),
            year = d.getFullYear(),
            dateArgs = [
                year,
                quarters[q],
                1
            ];

        return new Date(...dateArgs).getTime();
    }

getStartOfSemester.js

const getStartOfSemester = date => {
        const
            d = date ? new Date(date) : new Date(),
            semester = Math.ceil((d.getMonth() + 1) / 6),
            year = d.getFullYear(),
            dateArgs = [
                year,
                semester === 1 ? 1 : 7,
                1
            ];

        return new Date(...dateArgs).getTime();
    }