code: function computeRateBetweenSubunitAmounts(fromCurrency, fromAmount, toCurrency, toAmount) {
    /*
     * If currencies are equal, rate is 1
     */
    if (fromCurrency === toCurrency) {
      return 1;
    }
  
    /*
     * If toAmount is 0, we don't want to divide by zero.
     * In this case, return NaN
     */
    if (toAmount === 0) {
      return NaN;
    }
  
    /*
     * Convert both amounts to main units
     */
    const fromAmountMainUnit = fromSmallestSubunit(fromAmount, fromCurrency);
    const toAmountMainUnit = fromSmallestSubunit(toAmount, toCurrency);
  
    /*
     * Compute and return rate
     */
    return fromAmountMainUnit / toAmountMainUnit;
  }
docs: Computes a rate between two amounts in two different currencies.
  
  The result is fromAmount / toAmount (in the main units of their respective currencies)
  
  @param {string} fromCurrency
  @param {int} fromAmount Amount denominated in smallest sub-unit of fromCurrency
  @param {string} toCurrency
  @param {int} toAmount Amount denominated in smallest sub-unit of toCurrency