function _decimalPlaces(x) {
    if (!isNumberFinite(x)) {
        return;
    }
    let e = 1;
    let p = 0;
    while(Math.round(x * e) / e !== x){
        e *= 10;
        p++;
    }
    return p;
}
Returns the number of decimal places
i.e. the number of digits after the decimal point, of the value of this Number.
@param x - A number.
@returns The number of decimal places.
@private