re-organize attachment functions and updated comments doc

browser/lib/utils.js

@@ -136,9 +136,24 @@ export function isMarkdownTitleURL (str) {
   return /(^#{1,6}\s)(?:\w+:|^)\/\/(?:[^\s\.]+\.\S{2}|localhost[\:?\d]*)/.test(str)
 }
 
+export function humanFileSize (bytes) {
+  const threshold = 1000
+  if (Math.abs(bytes) < threshold) {
+    return bytes + ' B'
+  }
+  var units = ['kB', 'MB', 'GB', 'TB', 'PB', 'EB', 'ZB', 'YB']
+  var u = -1
+  do {
+    bytes /= threshold
+    ++u
+  } while (Math.abs(bytes) >= threshold && u < units.length - 1)
+  return bytes.toFixed(1) + ' ' + units[u]
+}
+
 export default {
   lastFindInArray,
   escapeHtmlCharacters,
   isObjectEqual,
-  isMarkdownTitleURL
+  isMarkdownTitleURL,
+  humanFileSize
 }