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inspect: add Temporal support #63154

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inspect: add Temporal support #63154

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50 changes: 50 additions & 0 deletions lib/internal/util/inspect.js
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Original file line number Diff line number Diff line change
Expand Up @@ -218,6 +218,47 @@ const builtInObjects = new SafeSet(
// https://tc39.es/ecma262/#sec-IsHTMLDDA-internal-slot
const isUndetectableObject = (v) => typeof v === 'undefined' && v !== undefined;

const temporalConstructors = [
{ name: 'Duration', fullName: 'Temporal.Duration' },
{ name: 'Instant', fullName: 'Temporal.Instant' },
{ name: 'PlainDate', fullName: 'Temporal.PlainDate' },
{ name: 'PlainDateTime', fullName: 'Temporal.PlainDateTime' },
{ name: 'PlainMonthDay', fullName: 'Temporal.PlainMonthDay' },
{ name: 'PlainTime', fullName: 'Temporal.PlainTime' },
{ name: 'PlainYearMonth', fullName: 'Temporal.PlainYearMonth' },
{ name: 'ZonedDateTime', fullName: 'Temporal.ZonedDateTime' },
];

// Best-effort, using instanceof. Polyfills will likely pass these checks.
// Returns void if either the type checks fail or the attempt at calling
// .toString() fails, so that format() can fall back to standard object
// formatting in either case.
// TODO: Hopefully the V8 API will expose typechecks at some point.
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@ljharb ljharb May 6, 2026

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Temporal itself exposes type checks via internal slots and builtin methods.

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@Renegade334 Renegade334 May 6, 2026

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Yes, but we can't guarantee a non-mutable path to get our hands on those methods.

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@ljharb ljharb May 6, 2026

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of course we can, via primordials

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@Renegade334 Renegade334 May 6, 2026

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Not while Temporal remains an optional feature, unfortunately.

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@ljharb ljharb May 6, 2026

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it's not? node 26 ships it unconditionally.

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@Renegade334 Renegade334 May 6, 2026

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It's enabled by default, but remains behind both runtime (cf. --no-harmony-temporal) and build flags, so this is unlikely to change any time soon.

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@ljharb ljharb May 6, 2026

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ahhh gotcha. surely we can still capture the builtins at startup, though, even if they're not real primordials yet?

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@Renegade334 Renegade334 May 6, 2026 •
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It's too early. Attempting to capture the global with something like const { Temporal } = globalThis in the header of inspect.js always hits thin air (I guess it's snapshotted?). We have to do it lazily from inspect(), at which point anything that intends to modify the Temporal global (polyfills etc.) will almost certainly already have run.

We could go full ham to hack around this, but it's not really a huge issue in the context of a function which only uses those methods to decide what flavour of human-readable output gets generated.

function getTemporalInfo(value) {
try {
const { Temporal } = globalThis;
if (Temporal === undefined) {
return;
}
for (let i = 0; i < temporalConstructors.length; i++) {
const entry = temporalConstructors[i];
const constructor = Temporal[entry.name];
if (typeof constructor !== 'function') {
return;
}
if (!FunctionPrototypeSymbolHasInstance(constructor, value)) {
continue;
}
const { prototype } = constructor;
if (!ObjectPrototypeHasOwnProperty(prototype, 'toString')) {
return;
}
const result = FunctionPrototypeCall(prototype.toString, value);
return { ...entry, result };
}
} catch { /* void */ }
}

// These options must stay in sync with `getUserOptions`. So if any option will
// be added or removed, `getUserOptions` must also be updated accordingly.
const inspectDefaultOptions = ObjectSeal({
Expand Down Expand Up @@ -1321,6 +1362,7 @@ function formatRaw(ctx, value, recurseTimes, typedArray) {
if (noIterator) {
keys = getKeys(value, ctx.showHidden);
braces = ['{', '}'];
let temporalInfo;
if (typeof value === 'function') {
base = getFunctionBase(ctx, value, constructor, tag);
if (keys.length === 0 && protoProps === undefined)
Expand Down Expand Up @@ -1404,6 +1446,14 @@ function formatRaw(ctx, value, recurseTimes, typedArray) {
if (keys.length === 0 && protoProps === undefined) {
return base;
}
} else if ((temporalInfo = getTemporalInfo(value))) {
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@aduh95 aduh95 May 8, 2026

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Don't we want to avoid calling getTemporalInfo more than once?

Suggested change
} else if ((temporalInfo = getTemporalInfo(value))) {
} else if ((temporalInfo ??= getTemporalInfo(value))) {

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@Renegade334 Renegade334 May 8, 2026

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This would be better called something like temporalToStringResult(value) – it's the combined type-check and stringification step for the inspect target.

const prefix = constructor === temporalInfo.name && tag === temporalInfo.fullName ?
(temporalInfo.fullName + ' ') :
getPrefix(constructor, tag, temporalInfo.fullName);
base = `${prefix}${temporalInfo.result}`;
if (keys.length === 0 && protoProps === undefined) {
return ctx.stylize(base, 'date');
}
} else {
if (keys.length === 0 && protoProps === undefined) {
if (isExternal(value)) {
Expand Down
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