is my die balanced?

die-fairness.js

// determines number of times you should roll a die to determine if it is "fair"
const find_number_of_rolls = (number_of_sides, required_confidence) => {
    const allowed_deviation = 1 - required_confidence
    const expected_value_per_side = 1/allowed_deviation
    const rolls = expected_value_per_side * number_of_sides

    return Math.round(rolls)
}

// rolls array takes the form: value_of_side(int)[]
// this expects that the values per side should be commensurate with required confidence
const is_die_biased = (rolls_array, required_confidence) => {
    const allowed_deviation = 1 - required_confidence
    const expected_value_per_side = 1/allowed_deviation

    const max = Math.round(expected_value_per_side + (expected_value_per_side*allowed_deviation))
    const min = Math.round(expected_value_per_side - (expected_value_per_side*allowed_deviation))

    return !rolls_array.every((current, index) => {
        if(current <= max && current >= min) {
            return true
        }
        else {
            console.warn(`die is unbalanced on side ${index+1}`)
            return false
        }
    })
}

const number_of_sides = 20
const required_confidence = 0.8

const rolls_array80correct = [
    5,5,4,6,5,
    5,5,4,6,5,
    5,5,4,6,5,
    5,5,4,6,5,
]

const rolls_array90correct = [
    9,10,11,9,10,
    9,10,11,9,10,
    9,10,11,9,10,
    9,10,11,9,10,
]

const rolls_array80bad = [
    5,5,4,6,5,
    5,5,42,6,5,
    5,5,4,6,5,
    5,5,4,6,5,
]

const rolls_array90bad = [
    9,10,11,9,10,
    9,10,11,9,10,
    9,10,11,1,10,
    9,10,11,9,10,
]

console.assert(find_number_of_rolls(20, 0.8) === 100)
console.assert(find_number_of_rolls(20, 0.95) === 400)

console.assert(is_die_biased(rolls_array80correct, 0.8) === false)
console.assert(is_die_biased(rolls_array90correct, 0.9) === false)
console.assert(is_die_biased(rolls_array80bad, 0.8) === true)
console.assert(is_die_biased(rolls_array90bad, 0.9) === true)