Cannot read properties of undefined (reading 'fallthrough')

[rogadev]

Describe the bug

I implemented a Promise.all() in a shadow endpoint that hits 2 different external API endpoints before it combines and returns the data. While the app doesn't seem to be breaking, I am getting the following error in my console when running in development.

Cannot read properties of undefined (reading 'fallthrough')
TypeError: Cannot read properties of undefined (reading 'fallthrough')
    at validate_shadow_output (file:///E:/LocalDevelopmentFiles/viu-fe/svelte/.svelte-kit/runtime/server/index.js:2759:13)
    at load_shadow_data (file:///E:/LocalDevelopmentFiles/viu-fe/svelte/.svelte-kit/runtime/server/index.js:2694:38)      
    at async load_node (file:///E:/LocalDevelopmentFiles/viu-fe/svelte/.svelte-kit/runtime/server/index.js:2285:5)        
    at async respond$1 (file:///E:/LocalDevelopmentFiles/viu-fe/svelte/.svelte-kit/runtime/server/index.js:2986:15)       
    at async resolve (file:///E:/LocalDevelopmentFiles/viu-fe/svelte/.svelte-kit/runtime/server/index.js:3456:11)
    at async respond (file:///E:/LocalDevelopmentFiles/viu-fe/svelte/.svelte-kit/runtime/server/index.js:3392:20)
    at async file:///E:/LocalDevelopmentFiles/viu-fe/svelte/node_modules/@sveltejs/kit/dist/vite.js:1555:22

Reproduction

https://github.com/rogadev/viu-fe/tree/for-svelte-bug

Logs

Cannot read properties of undefined (reading 'fallthrough')
TypeError: Cannot read properties of undefined (reading 'fallthrough')
    at validate_shadow_output (file:///E:/LocalDevelopmentFiles/viu-fe/svelte/.svelte-kit/runtime/server/index.js:2759:13)
    at load_shadow_data (file:///E:/LocalDevelopmentFiles/viu-fe/svelte/.svelte-kit/runtime/server/index.js:2694:38)      
    at async load_node (file:///E:/LocalDevelopmentFiles/viu-fe/svelte/.svelte-kit/runtime/server/index.js:2285:5)        
    at async respond$1 (file:///E:/LocalDevelopmentFiles/viu-fe/svelte/.svelte-kit/runtime/server/index.js:2986:15)       
    at async resolve (file:///E:/LocalDevelopmentFiles/viu-fe/svelte/.svelte-kit/runtime/server/index.js:3456:11)
    at async respond (file:///E:/LocalDevelopmentFiles/viu-fe/svelte/.svelte-kit/runtime/server/index.js:3392:20)
    at async file:///E:/LocalDevelopmentFiles/viu-fe/svelte/node_modules/@sveltejs/kit/dist/vite.js:1555:22

System Info

System:
    OS: Windows 10 10.0.19044
    CPU: (8) x64 Intel(R) Core(TM) i7-9700K CPU @ 3.60GHz
    Memory: 67.12 GB / 79.94 GB
  Binaries:
    Node: 18.3.0 - C:\Program Files\nodejs\node.EXE
    Yarn: 1.22.5 - C:\Program Files (x86)\Yarn\bin\yarn.CMD
    npm: 8.5.5 - C:\Program Files\nodejs\npm.CMD
  Browsers:
    Chrome: 103.0.5060.134
    Edge: Spartan (44.19041.1266.0), Chromium (103.0.1264.71)
    Internet Explorer: 11.0.19041.1566
  npmPackages:
    @sveltejs/adapter-auto: next => 1.0.0-next.64
    @sveltejs/kit: next => 1.0.0-next.396
    svelte: ^3.44.0 => 3.49.0
    vite: ^3.0.0 => 3.0.3

Severity

annoyance

Additional Information

No response

[benmccann]

@rogadev I cannot access your repository. Please check that it's accessible in an incognito window

[rogadev]

Apologies. Give it a go, now.

[rogadev]

I haven't had my coffee - I didn't mean to close that. 🤦‍♂️

[rogadev]

Here it is.

I made a noob error and didn't actually do anything with the object I created inside the Promise.all(). This makes it work as intended:

return await Promise.all([p1, p2]).then((results) => {
    return {
      status: 200,
      body: {
        noc,
        title: results[1].title,
        jobs: results[1].jobs,
        requirements: results[1].requirements,
        duties: results[1].duties,
        outlook: results[0].outlook,
        outlook_verbose: results[0].outlook_verbose,
        trends: results[0].trends,
        province: 'British Columbia',
        eruid: 5900,
      },
    }
  })

HOWEVER, I would still argue that the error messaging needs work. The way I finally figured out what was going on was this little squiggle at the top of my file which I never even noticed.

This finally nudged me to realize that I was just resolving all the promises and then doing absolutely nothing with what that Promise.all() returned.

I hope this is somewhat helpful feedback... 🤷‍♂️