code: function wma(close, n = 5) {
      let result = []
      let len = close.length
      if (len === 0 || n <= 0) {
          return result
      }
      let avg = close[0]
      result.push(avg)
  
      let T_m = close[0]
      let div = n * (n + 1) / 2
      for (let i = 1;  i < len; i++) {
          if (i < n) {
              T_m += close[i]
              let sum = 0
              let d = 0
              for (let j = 0; j <= i; j++) {
                  sum += close[i - j] * (n - j)
                  d += (n - j)
              }
              avg = sum / d
          } else {
              avg += (n * close[i] - T_m) / div
              T_m += close[i] - close[i - n]
          }
          result.push(avg)
      }
      return result
  }
docs: Weighted moving average