Merge pull request #192 from bluej100/beforeFirstChunk

beforeFirstChunk callback, fixes #186

papaparse.js

@@ -379,6 +379,7 @@
 		this._rowCount = 0;
 		this._start = 0;
 		this._nextChunk = null;
+		this._chunkIndex = 0;
 		this._completeResults = {
 			data: [],
 			errors: [],
@@ -388,6 +389,14 @@
 
 		this.parseChunk = function(chunk)
 		{
+			if (this._chunkIndex == 0 && isFunction(this._config.beforeFirstChunk)) {
+				var result = this._config.beforeFirstChunk(chunk);
+				if (result !== undefined)
+					chunk = result;
+			}
+
+			this._chunkIndex++;
+
 			// Rejoin the line we likely just split in two by chunking the file
 			var aggregate = this._partialLine + chunk;
 			this._partialLine = "";

tests/test-cases.js

@@ -1309,6 +1309,7 @@ var CUSTOM_TESTS = [
 			var updates = 0;
 			Papa.parse("/tests/long-sample.csv", {
 				worker: true,
+				download: true,
 				chunkSize: 500,
 				step: function(response, handle) {
 					updates++;
@@ -1319,5 +1320,26 @@ var CUSTOM_TESTS = [
 				}
 			});
 		}
+	},
+	{
+		description: "beforeFirstChunk can manipulate first chunk",
+		expected: 7,
+		run: function(callback) {
+			var updates = 0;
+			Papa.parse("/tests/long-sample.csv", {
+				download: true,
+				chunkSize: 500,
+				beforeFirstChunk: function(chunk) {
+					return chunk.replace(/.*?\n/, '');
+				},
+				step: function(response) {
+					updates++;
+				},
+				complete: function() {
+					callback(updates);
+				}
+			});
+		}
 	}
+
 ];