util.inspect shouldn’t format objects with the [[IsHTMLDDA]] internal slot as undefined

[ExE-Boss]

• Version: v13.9.0
• Platform: Windows 10 v1903 build 18362.657 64‑bit
• Subsystem: util

What steps will reproduce the bug?

Run node --allow-natives-syntax -p 'util.inspect(%GetUndetectable())'

What is the expected behavior?

> node --allow-natives-syntax -p 'util.inspect(%GetUndetectable())'
[Function (anonymous)]

What do you see instead?

> node --allow-natives-syntax -p 'util.inspect(%GetUndetectable())'
undefined

Additional information

This is because the type check in util.inspect doesn’t account for objects with the [[IsHTMLDDA]] internal slot:

node/lib/internal/util/inspect.js

Lines 681 to 688 in cdac185

	function formatValue(ctx, value, recurseTimes, typedArray) {
	// Primitive types cannot have properties.
	if (typeof value !== 'object' && typeof value !== 'function') {
	return formatPrimitive(ctx.stylize, value, ctx);
	}
	if (value === null) {
	return ctx.stylize('null', 'null');
	}

[devsnek]

I suppose this would matter when using electron, since you could actually do util.inspect(document.all). I can add an upstream Object::IsUndetectable and we could check it here.

We could also hack this in as typeof v === 'undefined' && v !== undefined.

[ExE-Boss]

One solution would be to add util.types.isObject(target), which would perform:

1. If Type(target) is Object, then return true.
2. Return false.

That would take care of that check, as C++ code doesn’t care whether an object is undetectable, since you can pass document.all as the this value to both Function.prototype.toString, Object.prototype.toString and Object.prototype.valueOf.

---

A polyfilled version is:

function isObject(target) {
	if (target === null || target === undefied) return false;
	switch (typeof target) {
		case "object":
		case "function":
			return true;
		case "undefined":
			try {
				return Object.prototype.valueOf.call(target) === target;
			} catch {}
	}
	return false;
}