support custom decoder option.

(used for cases when the encoding isn't supported by native buffer,  for example parsing 'SJIS'  in node)

docs/docs.html

@@ -429,6 +429,7 @@ var csv = Papa.unparse({
 	dynamicTyping: false,
 	preview: 0,
 	encoding: "",
+	decoder: undefined,
 	worker: false,
 	comments: false,
 	step: undefined,
@@ -530,6 +531,20 @@ var csv = Papa.unparse({
 									The encoding to use when opening local files. If specified, it must be a value supported by the FileReader API.
 								</td>
 							</tr>
+							<tr>
+								<td>
+									<code>decoder</code>
+								</td>
+								<td>
+									A function which allows custom decoding for the buffer string.
+									The function get Buffer and Encoding, and returns a string.
+									i.e assuming const iconv = require('iconv-lite'):
+									(buf , encoding) => {
+										if (iconv.encodingExists(encoding)) { return iconv.decode(buf, encoding) };
+										throw new TypeError('[ERR_UNKNOWN_ENCODING]', 'Unknown encoding: ' + encoding)	   
+									}							
+								</td>
+							</tr>
 							<tr>
 								<td>
 									<code>worker</code>

papaparse.js

@@ -852,7 +852,18 @@ License: MIT
 		{
 			try
 			{
-				queue.push(typeof chunk === 'string' ? chunk : chunk.toString(this._config.encoding));
+				var encoding = this._config.encoding;
+				var decoder = this._config.decoder;
+				var encodedString = '';
+
+				if (typeof decoder === 'function') {
+					encodedString = decoder(chunk, encoding);
+				} else if (typeof chunk === 'string') {
+					encodedString = chunk;
+				} else {
+					encodedString = chunk.toString(encoding);
+				}
+				queue.push(encodedString);
 
 				if (parseOnData)
 				{
@@ -941,7 +952,19 @@ License: MIT
 			// when too many items have been added without their
 			// callback being invoked
 			parseCallbackQueue.push(bindFunction(function() {
-				this.parseChunk(typeof chunk === 'string' ? chunk : chunk.toString(config.encoding));
+				var encoding = config.encoding;
+				var decoder = config.decoder;
+				var encodedString = '';
+
+				if (typeof decoder === 'function') {
+					encodedString = decoder(chunk, encoding);
+				} else if (typeof chunk === 'string') {
+					encodedString = chunk;
+				} else {
+					encodedString = chunk.toString(encoding);
+				}
+
+				this.parseChunk(encodedString);
 				if (isFunction(callback)) {
 					return callback();
 				}