buffer: allow encoding param to collapse

Currently the signature is indexOf(val[, byteOffset[, encoding]])
Instead allow indexOf(val[, byteOffset][, encoding])
so that byteOffset does not need to be passed.

PR-URL: https://github.com/nodejs/node/pull/4803
Reviewed-By: James M Snell <jasnell@gmail.com>

lib/buffer.js

@@ -464,10 +464,14 @@ function slowIndexOf(buffer, val, byteOffset, encoding) {
 }
 
 Buffer.prototype.indexOf = function indexOf(val, byteOffset, encoding) {
-  if (byteOffset > 0x7fffffff)
+  if (typeof byteOffset === 'string') {
+    encoding = byteOffset;
+    byteOffset = 0;
+  } else if (byteOffset > 0x7fffffff) {
     byteOffset = 0x7fffffff;
-  else if (byteOffset < -0x80000000)
+  } else if (byteOffset < -0x80000000) {
     byteOffset = -0x80000000;
+  }
   byteOffset >>= 0;
 
   if (typeof val === 'string') {

test/parallel/test-buffer-indexof.js

@@ -110,6 +110,11 @@ assert.equal(
     Buffer(b.toString('binary'), 'binary')
     .indexOf(Buffer('d', 'binary'), 0, 'binary'), 3);
 
+// test optional offset with passed encoding
+assert.equal(new Buffer('aaaa0').indexOf('30', 'hex'), 4);
+assert.equal(new Buffer('aaaa00a').indexOf('3030', 'hex'), 4);
+
+
 {
   // test usc2 encoding
   const twoByteString = new Buffer('\u039a\u0391\u03a3\u03a3\u0395', 'ucs2');