Moon Phase

index.html

<script>

  Moon.phase('2018', '01', '19'); // returns `quarter-moon`

</script>

moon.js

// Original Snippet: https://gist.github.com/endel/dfe6bb2fbe679781948c
// Moon.phase('2018', '01', '19');

var Moon = {
  phase: function(year, month, day) {
    var c = e = jd = b = 0;

    if(month < 3) {
      year--;
      month += 12;
    }

    ++month;
    c = 365.25 * year;
    e = 30.6 * month;
    jd = c + e + day - 694039.09; // jd is total days elapsed
    jd /= 29.5305882; // divide by the moon cycle
    b = parseInt(jd); // int(jd) -> b, take integer part of jd
    jd -= b; // subtract integer part to leave fractional part of original jd
    b = Math.round(jd * 8); // scale fraction from 0-8 and round

    if(b >= 8) b = 0; // 0 and 8 are the same so turn 8 into 0

    switch(b) {
      case 0: return 'new-moon'; break;
      case 1: return 'waxing-crescent-moon'; break;
      case 2: return 'quarter-moon'; break;
      case 3: return 'waxing-gibbous-moon'; break;
      case 4: return 'full-moon'; break;
      case 5: return 'waning-gibbous-moon'; break;
      case 6: return 'last-quarter-moon'; break;
      case 7: return 'waning-crescent-moon'; break;
    }
  }
}