Calculate simple moving average in JavaScript.

index.js

/**
 * Calculate the simple moving average from stock prices.
 * @param {Array} prices - The list of prices.
 * @param {number} interval - The number of periods to calculate.
 * @return {Array} The list of SMA value.
 */
exports.simpleMovingAverage = (prices, interval) => {
  let index = interval - 1;
  const length = prices.length + 1;
  let results = [];

  while (index < length) {
    index = index + 1;
    const intervalSlice = prices.slice(index - interval, index);
    const sum = intervalSlice.reduce((prev, curr) => prev + curr, 0);
    results.push(sum / interval);
  }

  return results;
}