add example for reactive declaration with a function?

[lingtalfi]

Hi, I was trying this code and it didn't work:

   let uFiles = [];
   $: totalSize = getTotalSize();

    function getTotalSize() {
        let total = 0;
        uFiles.forEach(uFile => {
            if (uFile.size) {
                total += uFile.size;
            }
        })
        return total;
    }

When I clicked a remove button which removed an uFile (by updating the uFiles array), the totalSize variable wasn't updated.
So I found that this was working:

    let uFiles = [];
    $: totalSize = getTotalSize(uFiles);

    function getTotalSize(_uFiles) {
        let total = 0;
        _uFiles.forEach(uFile => {
            if (uFile.size) {
                total += uFile.size;
            }
        })
        return total;
    }

Re-reading the docs, I saw that this was explained, but kind of hidden (https://svelte.dev/docs#3_$_marks_a_statement_as_reactive).

I believe adding an explicit example with a function call wouldn't hurt much, but would make things much easier to grab, rather than discovering through error/trial.

[dummdidumm]

There exists and explicit example of this in the docs now