convert non-buffer objects first to strings

btoa/index.js

@@ -2,7 +2,16 @@
   "use strict";
 
   function btoa(str) {
-    return new Buffer(str.toString(), 'binary').toString('base64');
+    var buffer
+      ;
+
+    if (str instanceof Buffer) {
+      buffer = str;
+    } else {
+      buffer = new Buffer(str.toString(), 'binary');
+    }
+
+    return buffer.toString('base64');
   }
 
   module.exports = btoa;