fix: avoid use of global (#4)

Related: socketio/socket.io-client#1166

index.js

@@ -7,8 +7,10 @@
 var isArray = require('isarray');
 
 var toString = Object.prototype.toString;
-var withNativeBlob = typeof global.Blob === 'function' || toString.call(global.Blob) === '[object BlobConstructor]';
-var withNativeFile = typeof global.File === 'function' || toString.call(global.File) === '[object FileConstructor]';
+var withNativeBlob = typeof Blob === 'function' ||
+                        typeof Blob !== 'undefined' && toString.call(Blob) === '[object BlobConstructor]';
+var withNativeFile = typeof File === 'function' ||
+                        typeof File !== 'undefined' && toString.call(File) === '[object FileConstructor]';
 
 /**
  * Module exports.
@@ -39,11 +41,11 @@ function hasBinary (obj) {
     return false;
   }
 
-  if ((typeof global.Buffer === 'function' && global.Buffer.isBuffer && global.Buffer.isBuffer(obj)) ||
-     (typeof global.ArrayBuffer === 'function' && obj instanceof ArrayBuffer) ||
-     (withNativeBlob && obj instanceof Blob) ||
-     (withNativeFile && obj instanceof File)
-    ) {
+  if ((typeof Buffer === 'function' && Buffer.isBuffer && Buffer.isBuffer(obj)) ||
+    (typeof ArrayBuffer === 'function' && obj instanceof ArrayBuffer) ||
+    (withNativeBlob && obj instanceof Blob) ||
+    (withNativeFile && obj instanceof File)
+  ) {
     return true;
   }