(Bugfix) Resolve issue where calling originalFetch can throw an unhandled rejection.

[Codex-]

This PR does the same change as #375 but I already made the change before noticing this PR and have some explanation around the fix 😅

Currently the existing code for processFetch calls originalFetch and stores the promise, it then attempts to attach a chain to the original promise to fork the promise resolution for raygun specific handling of things. This is fine except the catch is attached to the parent promise instead of the new then chain which has been added to the original promise.

This consequently means that if the newly attached then chain throws an exception it is not handled.

Original flow:

            ┌──────────────┐
            │ processFetch │
            └───────┬──────┘
                    │
                    ▼
┌─────────────────────────────────┐
│                                 │
│           ┌───────────────┐     │
│           │ originalFetch │     │
│           └───────┬───────┘     │
│                   │             │
│                   ▼             │
│              ┌─────────┐        │
│              │ promise │        │
│              └─┬──┬──┬─┘        │
│                │  │  │          │
│     ┌──────────┘  │  └──────┐   │
│     ▼             ▼         │   │
│ ┌──────┐      ┌───────┐     │   │
│ │ then │      │ catch │     │   │
│ └───┬──┘      └───────┘     │   │
│     │                       │   │
└─────┼───────────────────────┼───┘
      │                       │
   throws                  returns
      │                       │
      │                       ▼
      ▼                  ┌─────────┐
┌───────────┐            │ promise │
│ Unhandled │            └─────────┘
│           │
│ Rejection │
└───────────┘

This small change attaches the catch to the new then and handles throw errors as what appears to be the original intention of the code:

            ┌──────────────┐
            │ processFetch │
            └───────┬──────┘
                    │
                    ▼
┌─────────────────────────────────┐
│                                 │
│           ┌───────────────┐     │
│           │ originalFetch │     │
│           └───────┬───────┘     │
│                   │             │
│                   ▼             │
│              ┌─────────┐        │
│              │ promise │        │
│              └─┬─────┬─┘        │
│                │     │          │
│              ┌─┘     │          │
│              │       │          │
│              ▼       │          │
│          ┌──────┐    │          │
│          │ then │    │          │
│          └───┬──┘    │          │
│              │       │          │
│              ▼       │          │
│          ┌───────┐   │          │
│          │ catch │   │          │
│          └───────┘   │          │
│                      │          │
└──────────────────────┼──────────┘
                       │
                    returns
                       │
                       ▼
                  ┌─────────┐
                  │ promise │
                  └─────────┘

There are a number of other small oddities I noticed when tracking this down in this prototype that I will submit another PR for as they are not related to this immediate fix.

Fixes #430
Fixes fetch calls throwing outside of their calling try/catch #366

[Codex-]

We're currently trying to trial Raygun as a solution and keep hitting this issue preventing us from giving it a thorough run 😅 any feedback or review is appreciated 😄

[Olwiba]

Great work here @Codex-! appreciate the explanation & the diagrams 🤩
I've created a prerelease from your fork for you to test out, you can use the following snippet to make use of your changes while we go through the testing process on our end.

<script type="text/javascript">
    !function(a,b,c,d,e,f,g,h){a.RaygunObject=e,a[e]=a[e]||function(){
    (a[e].o=a[e].o||[]).push(arguments)},f=b.createElement(c),g=b.getElementsByTagName(c)[0],
    f.async=1,f.src=d,g.parentNode.insertBefore(f,g),h=a.onerror,a.onerror=function(b,c,d,f,g){
    h&&h(b,c,d,f,g),g||(g=new Error(b)),a[e].q=a[e].q||[],a[e].q.push({
    e:g})}}(window,document,"script","//cdn.raygun.io/raygun4js/prerelease/2.26.0-a/raygun.min.js","rg4js");
</script>

I've also updated your trial end date (12 Dec) to ensure you get to properly test out Raygun!

Always love seeing community submissions on our OSS & I'd love to say thank you!
Send me an email at ollie@raygun.com and we can get a goodie box sent out to you 😄

[Codex-]

Great work here @Codex-! appreciate the explanation & the diagrams 🤩 I've created a prerelease from your fork for you to test out, you can use the following snippet to make use of your changes while we go through the testing process on our end.

Thanks for this, although I did a quick check over the new minified code and found the patch has not been applied 😭 :

var i = c.apply(null, arguments);
try {
    var s = { method: n, requestURL: r, baseUrl: a };
    t && t.body && (s.body = t.body),
    u.executeHandlers(u.requestHandlers, s),
        i.then(
            ...
        ),
        i.catch(
            ...
        );

Where i is that of the original variable promise.

I've also updated your trial end date (12 Dec) to ensure you get to properly test out Raygun!

Thank you, we really appreciate it.

Always love seeing community submissions on our OSS & I'd love to say thank you! Send me an email at ollie@raygun.com and we can get a goodie box sent out to you 😄

Will do 😄

[Olwiba]

Apologies - try now @Codex-, I had originally built the master branch from your fork. The snippet should now target the bugfix/fetch_unhandled_rejection branch in your fork.

I also tried to build the feature/fetch_handling_improvements branch so I could upload this too but linting failed at src/raygun.network-tracking.js line 240 - 'originalFetch' is not defined.

[Codex-]

Great! Thanks for doing that, i'll take another look at that PR :)

[Olwiba]

You should be able to build the provider with grunt build from the root dir, this will run jshint to lint the updates

[Codex-]

Yup found the grunt script and got it working, almost nostalgic using grunt again 😅, building now and some more diagrams added to that PR, let's move that discussion over there 👍

[darcythomas]

All good, thanks :D

[darcythomas]

This has now been released to production :D

[Codex-]

awesome, thanks!