move market version tokens outside of func

Author: kimxogus

src/getLatestVersion.js

@@ -50,24 +50,24 @@ function getStoreUrl() {
   });
 }
 
+const MARKETVERSION_STARTTOKEN = "softwareVersion\">";
+const MARKETVERSION_STARTTOKEN_LENGTH = MARKETVERSION_STARTTOKEN.length;
+const MARKETVERSION_ENDTOKEN = "<";
 function getLatestVersionFromUrl(url, fetchOptions) {
   return fetch(url, fetchOptions)
     .then(res => {
       return res.text();
     })
     .then((text) => {
-      const startToken = "softwareVersion\">";
-      const endToken = "<";
-
-      const indexStart = text.indexOf(startToken);
+      const indexStart = text.indexOf(MARKETVERSION_STARTTOKEN);
       if (indexStart === -1) {
         latestVersion = text.trim();
         return Promise.resolve(latestVersion);
       }
 
-      text = text.substr(indexStart + startToken.length);
+      text = text.substr(indexStart + MARKETVERSION_STARTTOKEN_LENGTH);
 
-      const indexEnd = text.indexOf(endToken);
+      const indexEnd = text.indexOf(MARKETVERSION_ENDTOKEN);
       if (indexEnd === -1) {
         return Promise.reject("Parse error.");
       }