Ver.3 実行月の日曜始まり5週カレンダーを出力するJS / もっとシンプルに。中心に来る週を指定できるように

calendar.js

var Calendar = {};

Calendar.create = function(year, month, baseWeek, amplitude) {
  if (amplitude == undefined) amplitude = 2;
  var weeks = {};
  weeks['amplitude'] = amplitude;
  weeks['weekCount'] = amplitude*2 +1;
  
  for (var i=0; i<weeks['weekCount']; i++) {
    var week = [];
    var weekI = baseWeek +i-amplitude;
    var weekTop = new Date(year, month-1, 7*(weekI-1)+1);
    
    for (var j=0; j<7; j++) {
      week[j] = new Date(weekTop.getFullYear(), weekTop.getMonth(), weekTop.getDate() +j);
    }
    
    weeks[i] = week;
  }
  
  return weeks;
};

var today = new Date();
var weeks = Calendar.create(today.getFullYear(), today.getMonth()+1, today.getDate()/7);

window.onload = function() {
  var table = document.createElement('table');
  
  for (var i=0; i<weeks['weekCount']; i++) {
    var weektr = document.createElement('tr');
    
    for (var j=0; j<7; j++) {
      var datetd = document.createElement('td');
      var date = weeks[i][j];
      var mn = date.getMonth() +1;
      if (mn < 10) mn = '0' + mn;

      var dt = date.getDate();
      if (dt < 10) dt = '0' + dt;
      
      datetd.dataset.date = date.getFullYear() + '-' + mn + '-' + dt;
      datetd.innerText = date.getDate();
      weektr.appendChild(datetd);
    }
    
    table.appendChild(weektr);
  }
  
  document.body.appendChild(table);
};