You can create a multiplatform app with Phonegap. At https://build.phonegap.com you can also compile the app and generate ipa/apk files. If you want, of course, to publish it on iTunes/Google Play you have to use a certificate. Here, how to create&use an iOS certificate.
In my app, I need to download a pdf file from my api (base64 encoded, here how to create it), convert it and finally open it. Here how I made it.
I needed to create a simple FAQ page for my Phonegapp app. I found a lot of sample, but all of them were too complicated, I was searching for a simple one.
It took long time for me to manage in the correct way push notifications within my app. Using DevExtreme, I’m able to create a single app both for Android and iOS.
To test the push notifications feature, I use FCM (Firebase Cloud Messaging, by Google).