refactor + documentation

content.js

@@ -1,7 +1,7 @@
-
-
 // Get stored word list from chrome storage
 chrome.storage.local.get(["vocabulary", "kanji", "validUserLevel"], (data) => {
+    // The users level is not valid, e.g. it exceeds the maximum allowed level
+    // WaniKani requires that devs check if users are actually allowed to access content of this level
     if(!data.validUserLevel)
         return
 

popup.js

@@ -1,10 +1,12 @@
 const submitButton = document.getElementById("submit-token")
 const inputField = document.getElementById("token");
 
+// Set the wanikani token
 submitButton.addEventListener( "click", () => {
     chrome.storage.local.set({"token": inputField.value})
 })
 
+// Sync local data with wanikani
 const downloadButton = document.getElementById("download")
 downloadButton.addEventListener("click", async () => {
     var loadingText = document.getElementById("loading")
@@ -18,6 +20,7 @@ downloadButton.addEventListener("click", async () => {
         })
 })
 
+// Display currently used wanikani level
 chrome.storage.local.get("level", (data) => {
     const levelSpan = document.getElementById("level")
     levelSpan.innerHTML = data.level