JavaScript number precision in math operations

number.js

Object.defineProperties(Number.prototype, {
    add: {
        value: function (num, digitPrecision = 2) {
            return parseFloat((this + num).toFixed(digitPrecision))
        }
    },
    sub: {
        value: function (num, digitPrecision = 2) {
            return parseFloat((this - num).toFixed(digitPrecision))
        }
    },
    mul: {
        value: function (num, digitPrecision = 2) {
            return parseFloat((this * num).toFixed(digitPrecision))
        }
    },
    div: {
        value: function (num, digitPrecision = 2) {
            return parseFloat((this / num).toFixed(digitPrecision))
        }
    },
    mod: {
        value: function (num, digitPrecision = 2) {
            return parseFloat((this % num).toFixed(digitPrecision))
        }
    }
})