1509839 - chrome.runtime.sendMessage send undefined value

Status: RESOLVED INVALID

(WebExtensions :: General, defect)

Description

[NN]

User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:63.0) Gecko/20100101 Firefox/63.0

Steps to reproduce:

In content script of extension write the following code:
chrome.runtime.sendMessage({a:1, b:undefined})

In background script listen to message and print
chrome.runtime.onMessage.addListener(console.log)


Actual results:

Output is:
{a:1, b:undefined}

Firefox unlike Chrome passes undefined value between content script and background script.


Expected results:

The object should be JSON-ified thus removing all undefined values.
Expecting output:
{a:1}

Comment 1

[Kris Maglione [:kmag]]

This is the expected behavior.

Comment 2

[André Bargull [:anba]]

Does <https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions/API/runtime/sendMessage#Parameters> need to be updated? It currently describes that the "message" parameter is an object that can be serialized to JSON, which can be read that the message is actually serialized to JSON. And under JSON serialization, |undefined| properties are omitted by default.

Comment 3

[Kris Maglione [:kmag]]

Yes,that is inaccurate. sendMessage uses structured clone serialization, not JSON serialization.

Comment 4

[NN]

Any reason for this behavior ?
This breaks compatibility with other browsers supporting WebExtensions.

Comment 5

[Kris Maglione [:kmag]]

I can't imagine that it breaks compatibility with other browsers in any meaningful way. In any case, we've never aimed to be bug-for-bug compatible, especially not when it would mean a difficult-to-implement deviation from the structured clone specification for no obvious gain.

Comment 6

[NN]

My code sends an object where several values are not initialized.
In Edge and Chrome I didn't see any problem since they threw away keys having undefined values.
But in FF it sends the object with undefined values and it broke my code in background script which didn't expect undefined in any value.

Comment 7

[Chris Mills [:cmills]]

Updated page to say structured clone serialized, not JSON serialized. Better?