[request] Clearer error message for JSON deserialization failure (#2195)

docs/change-log.md

@@ -32,6 +32,7 @@
 - API: Introduction of `m.redraw.sync()` ([#1592](https://github.com/MithrilJS/mithril.js/pull/1592))
 - API: Event handlers may also be objects with `handleEvent` methods ([#1939](https://github.com/MithrilJS/mithril.js/issues/1939)).
 - API: `m.route.link` accepts an optional `options` object ([#1930](https://github.com/MithrilJS/mithril.js/pull/1930))
+- API: `m.request` better error message on JSON parse error - ([#2195](https://github.com/MithrilJS/mithril.js/pull/2195), [@codeclown](https://github.com/codeclown))
 - API: `m.request` supports `timeout` as attr - ([#1966](https://github.com/MithrilJS/mithril.js/pull/1966))
 - Mocks: add limited support for the DOMParser API ([#2097](https://github.com/MithrilJS/mithril.js/pull/2097))
 - API: add support for raw SVG in `m.trust()` string ([#2097](https://github.com/MithrilJS/mithril.js/pull/2097))

request/request.js

@@ -162,7 +162,7 @@ module.exports = function($window, Promise) {
 
 	function deserialize(data) {
 		try {return data !== "" ? JSON.parse(data) : null}
-		catch (e) {throw new Error(data)}
+		catch (e) {throw new Error("Invalid JSON: " + data)}
 	}
 
 	function extract(xhr) {return xhr.responseText}

request/tests/test-request.js

@@ -494,7 +494,7 @@ o.spec("xhr", function() {
 				}
 			})
 			xhr({method: "GET", url: "/item"}).catch(function(e) {
-				o(e.message).equals("error")
+				o(e.message).equals("Invalid JSON: error")
 			}).then(done)
 		})
 		o("triggers all branched catches upon rejection", function(done) {