First of all, JS is not the hottest language of the web, it is the only language of the web. This fact will never change, and WASM is just another addition to it. In order to trigger WASM, you need JS. In order to interact with Web APIs, you need JS. WASM is code written in another language, compiled to an AST (don't worry what that is, it's just a code representation) and running on a low level in the JSVM (JavaScript Virtual Machine). WASM cannot replace JS, at least yet. And that will remain true for quite a while. As a result, if you want to do web-dev, JS should be the first language you learn and at which you excel.
Well, that's true at least in terms of what runs inside a browser. If you want to add animations or logic, JS will do the job. However, many people don't like JS for different reasons, so there are projects in order to use other languages, which compensate for JS's flaws, and then transpile (read: convert) the programs into JS code. One of the most prominent languages is TypeScript, which is a superset of JS and adds things, like typing and interfaces. Once you are confident with JS, I recommend taking a look at such a language in order to at least understand in what way JS is lacking and what some companies might require of you if you want to create web applications for them.
If you are truly interested in WASM and find an application for it in one of your projects, though, I recommend taking a look at the Rust language, which by now has an official WASM compiler target. It is a language which allows you to make many guarantees about compiled code and promotes very modern programming paradigms. It has a steep learning curve, but is all the more rewarding afterwards for any code you write.