This looks like code after being compiled and transpiled from something like Typescript and Babel, it’s not what the engineer actually wrote.
For people that are not programmers: this code probably was generated by a program based on a different, supposedly better code. This is done because many browsers will only execute legacy JavaScript, and that is a pain in the ass to work with, so people work with better different languages or newer versions of JavaScript and a program just translates that to the lagacy JavaScript that old browsers will support.