Race condition/out of order results possible when data.src is an async function

• System Information

  • Browser type and version Any (I’m on Chrome 94.0.4606.114)
  • OS type and version Any (I’m on Chrome OS)
  • WINDOWS: be sure to indicate which terminal you’re using – (i.e., cmd.exe, powershell, git- bash, cygwin, Ubuntu via windows subsystem for linux, etc…)
  • Node version (IF applicable)
    • Any error messages that may be in the console where you ran npm start
  • Any error messages in the JS console

• Describe the bug

I have a simple async data.src function like this in the config that gets autocomplete results from an endpoint. I’m also using a no-op search engine so I just rely on results from the endpoint.

...
src: async (query) => {
        const response = await fetch(url);
        let json = await response.json();
        
        ... // do processing on json
        return json;
}
...
searchEngine: (q, r) => r,
...

The problem is that if the endpoint returns things out of order the final displayed results could be old and not make sense with the query. In practice this happens a lot because the geolocation API I’m using is rather unreliable (in terms of speed).

• To Reproduce

This is difficult to reproduce because it requires an autocomplete endpoint/API to return results out of order. I’m using geoapify.

• Expected behavior

Results from the src function be rejected if newer results have already been returned, or else some workaround allowing old results to be rejected.

I have tried this workaround which does work, but leaves uncaught errors:

...
src: async (query) => {
        const sent_timestamp = (new Date()).getTime();

        const response = await fetch(url);
        let json = await response.json();
        
        // Reject out of order results
        if (sent_timestamp < newest_timestamp) {
            throw Error("Old results");
        }
        newest_timestamp = sent_timestamp;
        
        ... // do processing on json
        return json;
}
...

I’m new to promises/async so might be missing some other way to reject old results cleanly. But regardless I believe this should be handled automatically.

[folknor]

Returning an Error instead of throwing

Haha! Can’t believe I misread that in your code, silly me 😛 I didn’t even read the keyword throw, I just read the Error part and wrote my comment. Good thing accidentally helped you anyway!

[ethanhjennings]

Returning an Error instead of throwing it works just fine for me! Thanks! Also, FYI, I found jQuery autocomplete had this same issue and a fix was implemented: https://bugs.jqueryui.com/ticket/5982