Improve error handling for widget loader

docs/functions/_userback_widget.default.html

@@ -29,7 +29,7 @@ <h5>token: <span class="tsd-signature-type">string</span></h5></li>
 <h5><code class="tsd-tag ts-flagOptional">Optional</code> ubOptions: <a href="../interfaces/_userback_widget.UserbackOptions.html" class="tsd-signature-type" data-tsd-kind="Interface">UserbackOptions</a></h5></li></ul></div>
 <h4 class="tsd-returns-title">Returns <span class="tsd-signature-type">Promise</span><span class="tsd-signature-symbol">&lt;</span><a href="../interfaces/_userback_widget.UserbackWidget.html" class="tsd-signature-type" data-tsd-kind="Interface">UserbackWidget</a><span class="tsd-signature-symbol">&gt;</span></h4><aside class="tsd-sources">
 <ul>
-<li>Defined in <a href="https://github.com/userback/widget-js/blob/master/widget-js/widget.ts#L143">widget-js/widget.ts:143</a></li></ul></aside></li></ul></section></div>
+<li>Defined in <a href="https://github.com/userback/widget-js/blob/master/widget-js/widget.ts#L147">widget-js/widget.ts:147</a></li></ul></aside></li></ul></section></div>
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docs/functions/_userback_widget.getUserback.html

@@ -24,7 +24,7 @@ <h1>Function getUserback</h1></div>
 </div>
 <h4 class="tsd-returns-title">Returns <span class="tsd-signature-type">undefined</span><span class="tsd-signature-symbol"> | </span><a href="../interfaces/_userback_widget.UserbackWidget.html" class="tsd-signature-type" data-tsd-kind="Interface">UserbackWidget</a></h4><aside class="tsd-sources">
 <ul>
-<li>Defined in <a href="https://github.com/userback/widget-js/blob/master/widget-js/widget.ts#L209">widget-js/widget.ts:209</a></li></ul></aside></li></ul></section></div>
+<li>Defined in <a href="https://github.com/userback/widget-js/blob/master/widget-js/widget.ts#L215">widget-js/widget.ts:215</a></li></ul></aside></li></ul></section></div>
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widget-js/widget.ts

@@ -134,18 +134,25 @@ let USERBACK: UserbackWidget | undefined;
 
 /* eslint-enable no-unused-vars */
 // internal variable for storing a pending load of the widget to prevent loading the widget twice
+// When undefined, the widget is not currently loading.
 let UBLoadingPromise: Promise<UserbackWidget> | undefined;
 /*
  * UserbackWidgetLoader
  *
  * Provides a type-safe interface for initializing and retrieving the Userback object
+ * @param token - The Userback token to use for initialisation
+ * @param ubOptions - Optional configuration options for the Userback widget
+ * @returns A promise that resolves to the UserbackWidget object
  */
 export default function UserbackWidgetLoader(token: string, ubOptions?: UserbackOptions): Promise<UserbackWidget> {
     if (UBLoadingPromise) return UBLoadingPromise;
 
     UBLoadingPromise = new Promise((resolve, reject) => {
         // Validation
-        const error = (e: string | Event) => reject(new Error(e.toString()));
+        const error = (e: string | Event) => {
+            UBLoadingPromise = undefined;
+            return reject(typeof e === 'string' ? new Error(e) : e);
+        };
         if (typeof USERBACK !== 'undefined') {
             // eslint-disable-next-line no-console
             console.debug('Userback widget loaded twice, canceling initialisation');
@@ -195,11 +202,10 @@ export default function UserbackWidgetLoader(token: string, ubOptions?: Userback
         script.src = `https://static.${ubDomain}/widget/v1.js`;
         script.async = true;
         script.onload = onload;
-        script.onerror = error;
+        script.addEventListener('error', error);
         document.body.appendChild(script);
         return true;
     });
-    UBLoadingPromise.catch(() => { UBLoadingPromise = undefined; });
     return UBLoadingPromise;
 }