argon2-browser | Argon2 library compiled for browser runtime

Background:

Hello everyone, I'm working on an AJAX login function for a website and I'm trying to use the Argon2 KDF (library) to derive a (somewhat) resource-intensive secret in the browser itself from a user-provided password before it is sent to the server for verification. The site utilizes TLS so I think from a security standpoint this is kind of a moot point, but I'd rather the client do this part of the work rather than the server, and this is more of a learning experience than a production site anyway.

Question:

The example code correctly computes the hash within my project, verifiable by the output from console.log(h.hashHex), but I've tried dozens of ways to try to assign the value to a variable to use later in the same function. I realize a Promise is asynchronous so I'm sure I'm going wrong somewhere regarding threads. When debugging, the variable that should be a hex string is either still undefined or optimized away. I'm sure there's some simple thing I'm missing but looking at similar questions (1, 2, 3) I still can't get it to work and don't have too much experience in JavaScript. Thanks for your input!

Sample Code (Works)