Leaderboard.js

var Firebase = require("firebase")

class Leaderboard {
    constructor(firebaseURL) {
        this.firebase = new Firebase(firebaseURL)
        this.firebase.orderByChild("score").limitToLast(5).on("value", (value) => {
            this.scores = value.val()
        })
    }
    add(data) {
        if(!data.name || data.name.length > 3) {
            throw new Error("Requires a valid name.")
        } else if(!data.score || isNaN(data.score)) {
            throw new Error("Requires a valid score.")
        } else {
            this.firebase.push(data).setPriority(data.score)
        }
    }
    get() {
        return this.scores
    }
}

To use it, just pass it a URL to your firebase.

var leaderboard = new Leaderboard("https://ehgoodenough.firebaseio.com/scores")
leaderboard.add({name: "ACM", score: 300})
var scores = leaderboard.get()