Can someone suggest me a front-end files hierarchy structure?

I’m working on a project with HTML, Sass and Javascript. Can someone suggest me a file structure (I mean how to place the files )?

You only need structure really if you have (or planning to have in future) high number of files. The common convention is to have all the code that will be compiled/transpiled in src directory. In your case that would be scss files and probably JS if you transpile it with Babel for example. The output of transpilation process normally goes into build or dist folder, the folder that will be served to public.