Get the current phase of the moon, and adjust a sprite for it

thats-no-moon.js

const phases=[
    {"sprite-x":123, "sprite-y":987, phase:"new"},
    {"sprite-x":123, "sprite-y":987, phase:"wax-crescent-1"},
    {"sprite-x":123, "sprite-y":987, phase:"wax-crescent-2"},
    {"sprite-x":123, "sprite-y":987, phase:"wax-crescent-3"},
    {"sprite-x":123, "sprite-y":987, phase:"wax-crescent-4"},
    {"sprite-x":123, "sprite-y":987, phase:"wax-crescent-5"},
    {"sprite-x":123, "sprite-y":987, phase:"wax-crescent-6"},
    {"sprite-x":123, "sprite-y":987, phase:"quarter-1"},
    {"sprite-x":123, "sprite-y":987, phase:"wax-gibbous-1"},
    {"sprite-x":123, "sprite-y":987, phase:"wax-gibbous-2"},
    {"sprite-x":123, "sprite-y":987, phase:"wax-gibbous-3"},
    {"sprite-x":123, "sprite-y":987, phase:"wax-gibbous-4"},
    {"sprite-x":123, "sprite-y":987, phase:"full"},
    {"sprite-x":123, "sprite-y":987, phase:"wane-gibbous-1"},
    {"sprite-x":123, "sprite-y":987, phase:"wane-gibbous-2"},
    {"sprite-x":123, "sprite-y":987, phase:"wane-gibbous-3"},
    {"sprite-x":123, "sprite-y":987, phase:"wane-gibbous-4"},
    {"sprite-x":123, "sprite-y":987, phase:"wane-gibbous-5"},
    {"sprite-x":123, "sprite-y":987, phase:"wane-gibbous-6"},
    {"sprite-x":123, "sprite-y":987, phase:"quarter-3"},
    {"sprite-x":123, "sprite-y":987, phase:"wane-crescent-1"},
    {"sprite-x":123, "sprite-y":987, phase:"wane-crescent-2"},
    {"sprite-x":123, "sprite-y":987, phase:"wane-crescent-3"},
    {"sprite-x":123, "sprite-y":987, phase:"wane-crescent-4"},
    {"sprite-x":123, "sprite-y":987, phase:"wane-crescent-5"},
    {"sprite-x":123, "sprite-y":987, phase:"new"}
]

let newMoonBaseline = new Date('November 26, 2019 15:05:00')
let millisecondsInADay = 86400000
let lunarSynodicPeriod = 29.53049

let daysSinceNewMoon = ((new Date()) - newMoonBaseline) / millisecondsInADay
let pctOfCurrentCycle = (daysSinceNewMoon % lunarSynodicPeriod) / lunarSynodicPeriod

var phaseIndex = Math.round((phases.length - 1) * pctOfCurrentCycle)

console.log(phases[phaseIndex].phase)