toByteArray(): use cached length value

lib/b64.js

@@ -23,8 +23,9 @@ var Arr = (typeof Uint8Array !== 'undefined')
 
 function toByteArray (b64) {
   var i, j, l, tmp, placeHolders, arr
+  var len = b64.length
 
-  if (b64.length % 4 > 0) {
+  if (len % 4 > 0) {
     throw new Error('Invalid string. Length must be a multiple of 4')
   }
 
@@ -33,14 +34,13 @@ function toByteArray (b64) {
   // represent one byte
   // if there is only one, then the three characters before it represent 2 bytes
   // this is just a cheap hack to not do indexOf twice
-  var len = b64.length
   placeHolders = b64.charAt(len - 2) === '=' ? 2 : b64.charAt(len - 1) === '=' ? 1 : 0
 
   // base64 is 4/3 + up to two characters of the original data
-  arr = new Arr(b64.length * 3 / 4 - placeHolders)
+  arr = new Arr(len * 3 / 4 - placeHolders)
 
   // if there are placeholders, only get up to the last complete 4 chars
-  l = placeHolders > 0 ? b64.length - 4 : b64.length
+  l = placeHolders > 0 ? len - 4 : len
 
   var L = 0