Improve comments

1 files changed, 21 insertions, 5 deletions

diff --git a/projects/3-realtime-stocks/src/stock-data.js b/projects/3-realtime-stocks/src/stock-data.js
index c70e2b4..8c97604 100644
--- a/projects/3-realtime-stocks/src/stock-data.js
+++ b/projects/3-realtime-stocks/src/stock-data.js
@@ -1,23 +1,39 @@
 export const generateValue = () => {
+  // randomly generate either 1 or -1
   const plusOrMinus = Math.round(Math.random()) ? 1 : -1
+  // start at 1 and add [-0.5, 0.5]
   return 1 + plusOrMinus * Math.random() * 0.5
 }
 export const generateStartingPoints = (n, pollPeriod) => {
+  // For some reason JS doesn't have a proper range
+  // function, so we have to make a new Array full of
+  // "empty items" (wtf js?). This means we have to
+  // fill the array before we can use functional operators/loops
+  // on it. JS is weird.
   return new Array(n).fill(1).map((k, i) => {
     return {
       value: generateValue(),
-      datetime: Date.now() - (n - i) * 1000
+      // first entries should be oldest,
+      // so take (n - i) as the scaling
+      // factor on pollPeriod
+      datetime: Date.now() - (n - i) * pollPeriod
     }
   })
 }
 const N_STARTING_POINTS = 50
 
+// Note that the current implementation of this class
+// could be static or not a class at all.
+// Generally, data providers receive some type of dependency injection
+// through the constructor, so I left it like this.
 export class StockDataProvider {
-  constructor() {}
+  constructor(secretApiKey) {
+    // Note used, for dependency injection demo only
+    this.secretApiKey = secretApiKey
+  }
   subscribeToStockData(pollFrequency, callback) {
-    // generate 100 random points
-    // 15 minutes apart
-    let points = generateStartingPoints(N_STARTING_POINTS)
+    // generate 50 random points
+    let points = generateStartingPoints(N_STARTING_POINTS, pollFrequency)
     const pushCallback = () => {
       points.push({ value: generateValue(), datetime: Date.now() })
       points.shift()