At the time JS was created, Perl didn't have a this. A lot of the docs and books suggested using $self but a reference to the object would be passed as the first parameter to all class methods and you assign that to any name you wanted.

It's only very recently (as in the last year or so) with a new class system that Perl has hard-coded $self for that purpose.

this is commonly used with a similar meaning to self in cases where self can't be used because it is a reserved keyword.

Example:

    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<St1::Item>> {
        let this = self.project();
        this.inner.poll_next(cx)
    }

https://github.com/rust-lang/futures-rs/blob/master/futures-util/src/stream/select.rs#L113-L116