Where to use camelCase and where snake_case?

Question

JavaScript

Can you please tell me where and when to use each style?
For example, in JS I know this:
for constants known at the time of description: For constants calculated: But in general, if there is no style guide in the project, or the project is new, how to understand which and where to use the style?
const SNAKE_LENGTH = 12.5;
const windowHeight = window.outerHeight();

Answer 1

There must be style guides. If they are not there, take the popular ones for your language, they are always there.

Answer 2

https://github.com/rwaldron/idiomatic.js/