handle fetch request failure and throw error /w message 'Network error'

packages/amazon-cognito-identity-js/src/Client.js

@@ -40,6 +40,13 @@ export default class Client {
       .then(resp => {
         response = resp;
         return resp;
+      }, err => {
+        // If error happens here, the request failed
+        // if it is TypeError throw network error
+        if (err instanceof TypeError) {
+          throw new Error('Network error');
+        }
+        throw err;
       })
       .then(resp => resp.json().catch(() => ({})))
       .then(data => {
@@ -56,17 +63,32 @@ export default class Client {
         return callback(error);
       })
       .catch(err => {
-        if (err) {
-          return callback(err);
+        let code = 'UnknownError', error = {};
+
+        // first check if we have a service error
+        if ( response && response.headers && response.headers.get('x-amzn-errortype') ) {
+          try {
+              code = (response.headers.get('x-amz-errortype')).split(':')[0];
+              error = {
+                  code,
+                  name: code,
+                  statusCode: response.status,
+                  message: (response.status) ? response.status.toString() : null,
+                };
+          } catch( error ) { 
+              // pass through so it doesn't get swallowed if we can't parse it 
+          }
+        // otherwise check error
+        } else if ( err instanceof Error ) {
+            error = {
+                code: err.name,
+                name: err.name,
+                message: err.message
+            };
+        // finally case will return 'UnknownError'
+        } else {
+            error = { code };
         }
-        // Taken from aws-sdk-js/lib/protocol/json.js
-        const code = (response.headers.get('x-amzn-errortype') || 'UnknownError').split(':')[0];
-        const error = {
-          code,
-          name: code,
-          statusCode: response.status,
-          message: response.status.toString(),
-        };
         return callback(error);
       });
   }