refactor: reuse unsafe header regex pattern

Author: rexxars

lib/eventsource.js

@@ -16,6 +16,8 @@ var lineFeed = 10
 var carriageReturn = 13
 // Beyond 256KB we could not observe any gain in performance
 var maxBufferAheadAllocation = 1024 * 256
+// Headers matching the pattern should be removed when redirecting to different origin
+var reUnsafeHeader = /^(cookie|authorization)$/i
 
 function hasBom (buf) {
   return bom.every(function (charCode, index) {
@@ -482,7 +484,7 @@ function MessageEvent (type, eventInitDict) {
 function removeUnsafeHeaders (headers) {
   var safe = {}
   for (var key in headers) {
-    if (/^(cookie|authorization)$/i.test(key)) {
+    if (reUnsafeHeader.test(key)) {
       continue
     }