`ImageData` not stringifying consistently on Node 14.7

[brettz9]

Issue or Feature

In typeson-registry, we need to detect object type in order to properly serialize objects for JSON.

For some reason, on Node 14 in Linux (Xenial), this is failing, but it is not failing in Node 10 or 12 in Linux, nor in Node 14 on the Mac. This is failing on Node 14.7, but not in Node 10 or 12.

In performing some logging, it turns out that calling Object.prototype.toString.call() on ImageData objects will give [object Object] in Node 14.7, but in other environments, as expected, it gives [object ImageData].

Perhaps this is due to a proper fix in Node 14.7 since objects should only give [object Object] unless Symbol.toStringTag is used, but in any case, if it is not doing so already, I'd hope your build process could add the equivalent of the following to ImageData to ensure it behaves as in the browser so that one can detect the type of such objects (this approach will, unlike instanceof, also ensure detection continues to work cross-frame when used in polyglot browser code).

                get [Symbol.toStringTag] () {
                    return 'ImageData';
                }

Steps to Reproduce

const {ImageData} = require('canvas');
const imageData = new ImageData(1, 3);
console.log(Object.prototype.toString.call(imageData));
// Expected `[object ImageData]` but get `[object Object]` in Node 14 Linux

Your Environment

• Version of node-canvas (output of npm list canvas or yarn list canvas): 2.6.1
• Environment (e.g. node 4.2.0 on Mac OS X 10.8): Node 14.7 on Linux xenial or MacOSX; see the Travis job

Thanks!

[zbjornson]

This is probably related to #1639, which @asturur said is new since 14.7. Is you Mac running <14.7?

Think this is a straightforward fix I can work on in the coming week or two. Also happy to review a PR.

[brettz9]

Sorry, turns out I hadn't successfully switched nvm to Node 14. Am on a very slow/flaky connection, so can't really test Node 14 on the Mac locally again atm, but on Travis, it is giving the same [object Object] result as in Linux, so it appears it may indeed be a universal Node 14.7 problem.

Unfortunately, am not at all familiar with C/C++ (e.g., to see about adding Symbol.toStringTag in src/ImageData.*).

[brettz9]

I'm on v14.15.5 (through nvm) and still getting the issue.

[brettz9]

@zbjornson : Any chance you'd be free to take a look?

[brettz9]

bump...

[zbjornson]

Meant to make a PR but accidentally pushed the fix to master. Will be in the next release.

[brettz9]

@zbjornson : I'm still not seeing this work in the 2.9.1 release. Running Object.prototype.toString.call(new canvas.ImageData(1, 3)).slice(8, -1)) still gives "Object" instead of "ImageData".

[brettz9]

I think what the issue is in my case is that I am not running toString on the instance. I am using the class-type detection of Object.prototype.toString.call, which necessitates some code like:

                get [Symbol.toStringTag] () {
                    return 'ImageData';
                }

[brettz9]

Can you please reopen this? This is not fixed. Note that it is not a toString issue but toStringTag issue.

[brettz9]

Is there anything I can help clarify about this topic to speed it along? This should I think really be a no-brainer as it is consistent with browser behavior and is a minor addition.

toStringTag may not be required of all interfaces in web specs, but as Node itself agreed by implementing nodejs/node#45987 recently for another API, keeping consistency with browsers in this regard is beneficial to users. (Though not always implementing as toStringTag, browsers do produce the same result, and in JavaScript, toStringTag is the way to do it at this time).