🐛 BUG: Workers tail events turn `undefined` into `null`

[KianNH]

Which Cloudflare product(s) does this pertain to?

Workers Runtime

What version(s) of the tool(s) are you using?

n/a

What version of Node are you using?

n/a

What operating system are you using?

n/a

Describe the Bug

Workers tail events will turn undefined into null, which confuses users as these types don't overlap & issues such as if (undefined === null) are not picked up by TypeScript.

This isn't an issue with Wrangler specifically, the same behaviour is observed in the tail events shown in the dashboard.

Discord link: https://discord.com/channels/595317990191398933/779390076219686943/1149351316112539718

Please provide a link to a minimal reproduction

No response

Please provide any relevant error logs

No response

[Cherry]

I just hit this and spent far longer than I care to admit trying to debug it. It's especially problematic on nested object properties. As a simple repro:

export default {
	async fetch(request, env, ctx) {
		const response = await fetch('https://api.api-ninjas.com/v1/randomuser');
		const json = await response.json();
		console.log(json.test);
		return new Response('Hello World');
	},
};

via wrangler tail:

  (log) null

json.test is absolutely not null, which has a very different meaning in JavaScript than undefined.

[lrapoport-cf]

hi @KianNH and @Cherry , thanks for reporting this. i've raised this with the relevant internal team and they will look into this (internal ticket WP-850). as this is not a wrangler issue i'm going to close this issue, but i've linked it to the internal ticket and asked that any updates be reported back here as well :)

[markjmiller]

This is a tricky one. json can't represent javascript values such as undefined and NaN, so they have to be serialized to null. This trade-off was intentionally decided in the workers runtime. This could be solved with a new TailRequest method to convert serialized null values back to their original js value.

[Cherry]

Thanks @markjmiller.

Unfortunately, tail logs today without this distinction are at best, extremely difficult to use, and at worst, effectively useless. There is a a very strong difference in JavaScript between null and undefined, so this makes debugging extremely difficult, as per my trivial example above.