Some definition from

https://mahifx.com/mfxtrade/indicators/smoothed-moving-average-smma

methods/indicators/SMA.js

@@ -1,5 +1,24 @@
-// required indicators
+/**
+ * The first value for the Smoothed Moving Average is calculated as a Simple Moving Average (SMA):
+
+SUM1=SUM (CLOSE, N)
+
+SMMA1 = SUM1/ N
+
+The second and subsequent moving averages are calculated according to this formula:
 
+SMMA (i) = (SUM1 – SMMA1+CLOSE (i))/ N
+
+Where:
+
+SUM1 – is the total sum of closing prices for N periods;
+SMMA1 – is the smoothed moving average of the first bar;
+SMMA (i) – is the smoothed moving average of the current bar (except the first one);
+CLOSE (i) – is the current closing price;
+N – is the smoothing period.
+ */
+
+// required indicators
 var Indicator = function(weight) {
   this.weight = weight;
   this.prices = [];