function formatDate(date) {
      
        var year = date.getFullYear()
        var month = date.getMonth() + 1
        var day = date.getDate()

        return [year, month, day].map(formatNumber).join(’-’)
    }
    function formatNumber(n) {
        n = n.toString()
        return n[1] ? n : ‘0’ + n
    }

formatDate(new Date(‘2017-05-31 21:00:57’)) 返回是 ‘2017-06-01’