fix(api-load): Allow false for unload

Currently, only `true` and an array of strings are valid values for the property. While `false` does not add additional functionality, it removes an odd and unexpected behavior of triggering unload in the same form as if you were to pass `true`. Other than specifically not unloading when `false`, this change avoids opinionation of the value passed itself.

Fix #321
Close #333

AUTHORS.txt

@@ -14,3 +14,4 @@ dtc03012 <https://github.com/dtc03012>
 Kim Dong Min <https://github.com/haracejacob>
 Russell Shingleton <[email protected]>
 Matthias Komarek <https://github.com/matthiaskomarek>
+Tony Quetano <[email protected]>

src/api/api.load.js

@@ -25,7 +25,7 @@ extend(Chart.prototype, {
 	 *    | axes | The axes specified by data.axes will be updated. axes must be Object that has target id as keys. |
 	 *    | colors | The colors specified by data.colors will be updated. colors must be Object that has target id as keys. |
 	 *    | - type<br>- types | The type of targets will be updated. type must be String and types must be Object. |
-	 *    | unload | Specify the data will be unloaded before loading new data. If true given, all of data will be unloaded. If target ids given as String or Array, specified targets will be unloaded. |
+	 *    | unload | Specify the data will be unloaded before loading new data. If true given, all of data will be unloaded. If target ids given as String or Array, specified targets will be unloaded. If absent or false given, unload will not occur. |
 	 *    | done | The specified function will be called after data loaded.|
 	 *
 	 * @example
@@ -78,12 +78,10 @@ extend(Chart.prototype, {
 		}
 
 		// unload if needed
-		if ("unload" in args) {
+		if ("unload" in args && args.unload !== false) {
 			// TODO: do not unload if target will load (included in url/rows/columns)
-			$$.unload(
-				$$.mapToTargetIds(
-					isBoolean(args.unload) && args.unload ?
-						null : args.unload), () => $$.loadFromArgs(args)
+			$$.unload($$.mapToTargetIds(isBoolean(args.unload) && args.unload ? null : args.unload), () =>
+				$$.loadFromArgs(args)
 			);
 		} else {
 			$$.loadFromArgs(args);