Allow transforming header columns (#589)

* Deprecate trimHeaders: The same result can be achieved by using transformHeader parameter.

docs/docs.html

@@ -340,7 +340,7 @@ var csv = Papa.unparse({
 	quoteChar: '"',
 	escapeChar: '"',
 	header: false,
-	trimHeaders: false,
+	transformHeader: undefined,
 	dynamicTyping: false,
 	preview: 0,
 	encoding: "",
@@ -412,10 +412,10 @@ var csv = Papa.unparse({
 							</tr>
 							<tr>
 								<td>
-									<code>trimHeaders</code>
+									<code>transformHeader</code>
 								</td>
 								<td>
-									If true leading/trailing spaces will be trimed from headers.
+									A function to apply on each header. Requires <code>header</code> to be <code>true</code>. The function receives the header as its first argument.
 								</td>
 							</tr>
 							<tr>

papaparse.js

@@ -1151,8 +1151,8 @@ if (!Array.isArray)
 				{
 					var header = _results.data[i][j];
 
-					if (_config.trimHeaders) {
-						header = header.trim();
+					if (isFunction(_config.transformHeader)) {
+						header = _config.transformHeader(header);
 					}
 
 					_fields.push(header);

tests/test-cases.js

@@ -725,11 +725,11 @@ var PARSE_TESTS = [
 		}
 	},
 	{
-		description: "Header rows are trimmed when trimHeaders is set",
-		input: '  A , B  ,  C  \r\na,b ,c',
-		config: { header: true, trimHeaders: true },
+		description: "Header rows are transformed when transformHeader function is provided",
+		input: 'A,B,C\r\na,b,c',
+		config: { header: true, transformHeader: function(header) { return header.toLowerCase(); } },
 		expected: {
-			data: [{"A": "a", "B": "b ", "C": "c"}],
+			data: [{"a": "a", "b": "b", "c": "c"}],
 			errors: []
 		}
 	},