Stop jhr XHR function from swallowing JSON.parse error

.gitignore

@@ -1,3 +1,4 @@
 node_modules
 lib/*
 dist
+.idea

src/verbs.ts

@@ -1,5 +1,5 @@
-import { StringMap } from "./types";
-import { KeratinError } from "./types";
+import {StringMap} from "./types";
+import {KeratinError} from "./types";
 import formData from "./formData";
 
 export function get<T>(url: string, data: StringMap): Promise<T> {
@@ -33,7 +33,7 @@ function jhr<T>(sender: (xhr: XMLHttpRequest) => void): Promise<T> {
     xhr.withCredentials = true; // enable authentication server cookies
     xhr.onreadystatechange = () => {
       if (xhr.readyState == XMLHttpRequest.DONE) {
-        const data: {result?: T, errors?: KeratinError[]} = (xhr.responseText.length > 1) ? JSON.parse(xhr.responseText) : {};
+        const data = maybeParseJSON<T>(xhr.responseText);
 
         if (data.result) {
           fulfill(data.result);
@@ -52,3 +52,14 @@ function jhr<T>(sender: (xhr: XMLHttpRequest) => void): Promise<T> {
     sender(xhr);
   });
 }
+
+function maybeParseJSON<T>(response: string): { result?: T, errors?: KeratinError[] } {
+  if (response === '') {
+    return {}
+  }
+  try {
+    return JSON.parse(response)
+  } catch (err) {
+    return {errors: [{message: `HTTP response '${response}' is not JSON as expected: ${err}`}]}
+  }
+}

test/tests.js

@@ -261,6 +261,21 @@ QUnit.test("failure", function(assert) {
     });
 });
 
+QUnit.test("Non JSON XHR response", function(assert) {
+  this.server.respondWith('POST', 'https://authn.example.com/session',
+    'Origin is not a trusted host.'
+  );
+
+  const expectedError = "HTTP response 'Origin is not a trusted host.' is not JSON as expected: SyntaxError: " +
+    "JSON.parse: unexpected character at line 1 column 1 of the JSON data"
+
+  return KeratinAuthN.login({username: 'test', password: 'test'})
+    .then(refuteSuccess(assert))
+    .catch(function(errors) {
+      assert.deepEqual(errors, [{message: expectedError}]);
+    });
+});
+
 QUnit.module("requestPasswordReset", startServer);
 QUnit.test("success or failure", function(assert) {
   this.server.respondWith('GET', 'https://authn.example.com/password/reset?username=test', '');