cal.js/cal.js

/*

    ╔═════ juin 2017 ══════╤════ juillet 2017 ════╤══════ août 2017 ═════╗
    ║ lu ma me je ve sa di │ lu ma me je ve sa di │ lu ma me je ve sa di ║
    ╟──────────────────────┼──────────────────────┼──────────────────────╢
    ║           1  2  3  4 │                 1  2 │     1  2  3  4  5  6 ║
    ║  5  6  7  8  9 10 11 │  3  4  5  6  7  8  9 │  7  8  9 10 11 12 13 ║
    ║ 12 13 14 15 16 17 18 │ 10 11 12 13 14 15 16 │ 14 15 16 17 18 19 20 ║
    ║ 19 20 21 22 23 24 25 │ 17 18 19 20 21 22 23 │ 21 22 23 24 25 26 27 ║
    ║ 26 27 28 29 30       │ 24 25 26 27 28 29 30 │ 28 29 30 31          ║
    ║                      │ 31                   │                      ║
    ╚══════════════════════╧══════════════════════╧══════════════════════╝

*/

Array.prototype.chunk = Array.prototype.chunk || function(n) {
    return !this.length ? [] : [this.slice(0, n)].concat(this.slice(n).chunk(n))
}

const CalPrinter = date => {
    date = date || new Date

    const monthData = (date, offset) => {
        date = new Date((new Date).setMonth(date.getMonth() + (offset || 0)))

        const year = date.getFullYear()
        const month = date.toLocaleString('fr-FR', { month: 'long'})
        const text = ` ${month} ${year} `
        const padding = (22 - text.length) / 2
        const title = '═'.repeat(Math.floor(padding)) + text + '═'.repeat(Math.ceil(padding))

        let start = new Date(year, date.getMonth()).getDay() - 1
        start = start < 0 ? 6 : start
        const end = new Date(year, date.getMonth() + 1, 0).getDate()
        let dates = [...Array(end + 1).keys()].slice(1).map(n =>` ${n}`.slice(-2))
        const lines = [...Array(start).fill('  '), ...dates, ...Array(18).fill('  ') ]
            .chunk(7).map(c => ` ${c.join(' ')} `)

        return { title, lines }
    }

    const days = ' ' + [..."0123456"].map(n => (new Date(2017, 1, n + 6))
        .toLocaleString('fr-FR', { weekday: 'short' })
        .substr(0, 2)).join(' ') + ' '

    const months = [..."012"].map((v, i) => monthData(date, i))

    const printer = ({ days, months }) =>
`
    ╔${  months[0].title  }╤${  months[1].title  }╤${  months[2].title  }╗
    ║${        days       }│${        days       }│${        days       }║
    ╟──────────────────────┼──────────────────────┼──────────────────────╢
    ║${months[0].lines[0] }│${months[1].lines[0] }│${months[2].lines[0] }║
    ║${months[0].lines[1] }│${months[1].lines[1] }│${months[2].lines[1] }║
    ║${months[0].lines[2] }│${months[1].lines[2] }│${months[2].lines[2] }║
    ║${months[0].lines[3] }│${months[1].lines[3] }│${months[2].lines[3] }║
    ║${months[0].lines[4] }│${months[1].lines[4] }│${months[2].lines[4] }║
    ║${months[0].lines[5] }│${months[1].lines[5] }│${months[2].lines[5] }║
    ╚══════════════════════╧══════════════════════╧══════════════════════╝
`

    return printer.bind(null, { days, months })
}

console.log(CalPrinter()())