12 Days Challenge

12-days.js

let gifts = ["partridge in a pear tree", "turtle doves", "French hens", "calling birds", "gold rings", "geese a-laying", "swans a-swimming", "maids a-milking", "ladies dancing", "lords a-leaping", "pipers piping", "drummers drumming"]

let numLookup = [
 { cardinal: "a",      ordinal: "first"   },
 { cardinal: "two",    ordinal: "second"  },
 { cardinal: "three",  ordinal: "third"   },
 { cardinal: "four",   ordinal: "fourth"  },
 { cardinal: "five",   ordinal: "fifth"   },
 { cardinal: "six",    ordinal: "sixth"   },
 { cardinal: "seven",  ordinal: "seventh" },
 { cardinal: "eight",  ordinal: "eigth"   },
 { cardinal: "nine",   ordinal: "ninth"   },
 { cardinal: "ten",    ordinal: "tenth"   },
 { cardinal: "eleven", ordinal: "eleventh"},
 { cardinal: "twelve", ordinal: "twelfth" }
]

let dailyGift = (day) => {
    let count = numLookup[day].cardinal
    let gift = gifts[day]
    return `${count} ${gift}`
}

let toProperCase = s => s[0].toUpperCase() + s.substr(1)

let verses = gifts.map((el, i) => {
    let numText = numLookup[i].ordinal
    let chorus = `On the ${numText} day of Christmas\nMy true love gave to me`

    let cumDays = [...Array(i+1).keys()]
    let cumGift = cumDays.map(dailyGift)

    if (i>0) {cumGift[0] = `and ${cumGift[0]}`}

    let lines = cumGift.map(toProperCase).reverse().join('\n')

    let verse = `${chorus}\n${lines}.`
    return verse
})

let song = verses.join('\n\n')

console.log(song)

12-days.min.js

let gifts=["partridge in a pear tree","turtle doves","French hens","calling birds","gold rings","geese a-laying","swans a-swimming","maids a-milking","ladies dancing","lords a-leaping","pipers piping","drummers drumming"],
nums=[{c:"a",o:"first"},{c:"two",o:"second"},{c:"three",o:"third"},{c:"four",o:"fourth"},{c:"five",o:"fifth"},{c:"six",o:"sixth"},{c:"seven",o:"seventh"},{c:"eight",o:"eighth"},{c:"nine",o:"ninth"},{c:"ten",o:"tenth"},{c:"eleven",o:"eleventh"},{c:"twelve",o:"twelfth"}],
song=gifts.map((e,i)=>{
    let o=`On the ${nums[i].o} day of Christmas\nMy true love gave to me`
    let c=[...Array(i+1).keys()].map(e=>`${nums[e].c} ${gifts[e]}`)
    i>0&&(c[0]=`and ${c[0]}`)
    let l=c.map(e=>e[0].toUpperCase()+e.substr(1)).reverse().join("\n");
    return `${o}\n${l}.`
}).join("\n\n");
console.log(song);