code: function ema(close, n = 5) {
      let len = close.length
      let result = []
      if (len === 0 || n <= 0) {
          return result
      }
      let alpha = 2 / (n + 1)
      let avg = close[0]
      result.push(avg)
      for (let i = 1; i < len; i++) {
          avg = alpha * close[i] + (1 - alpha) * avg
          result.push(avg)
      }
      return result
  }
docs: Exponential moving average
  
  alpha = 2 / (N + 1)