Convert callback based asynchronous methods for more linear code, with Promises + Async/Await in JavaScript and Coroutines in Kotlin.
In JavaScript, wrap the callback based method inside a new Promise((resolve, reject) => {...}) call. Then call the resolve/reject method of the promise on callback completion. The result is an asynchronous promise that resolves with the result of the callback.
In Kotlin, wrap the callback based method inside a suspendCoroutine {continuation-> ...}. Then call continuation.resume or continuation.resumeWithException on callback completion. The result is an asynchronous/suspending Coroutine that returns the value of the callback.
A small drawback of these approaches is that they return a single value, while the callback can have multiple values. The solution to this is to wrap the values returned from the callback in an object (JS) or data class (Kotlin).