three-boxes.js

function randInt (n) {
    return Math.floor(Math.random() * n)
}

function randChoice (array) {
    return array[randInt(array.length)]
}

function allTheSame (array) {
    if (!array.length) {
        return true
    }
    return array.filter(v => v === array[0]).length === array.length
}

const boxes = [
    [0, 0],
    [0, 1],
    [1, 1],
]

const valueToTry = 0
const stats = {
    totalTries: 0,
    totalTriesMatchingValue: 0,
    totalInvalidTries: 0,
    totalMatches: 0,
    totalMismatches: 0,
}

function theTry (boxes, ballColor) {
    const randomBox = randChoice(boxes)
    stats.totalTries++
    const randomBall = randChoice(randomBox)
    if (randomBall !== ballColor) {
        stats.totalInvalidTries++
        return
    } else {
        stats.totalTriesMatchingValue++
        if (allTheSame(randomBox)) {
            stats.totalMatches++
        } else {
            stats.totalMismatches++
        }
    }
}

const numberOfTries = 5000

for (let i = 0; i < numberOfTries; i++) {
    theTry(boxes, valueToTry)
}

console.log(stats)
console.log(stats.totalMatches / stats.totalTriesMatchingValue)