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util: simplify constructor retrieval in inspect() #36466

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Dec 14, 2020
Merged

util: simplify constructor retrieval in inspect() #36466

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47 changes: 3 additions & 44 deletions lib/internal/util/inspect.js
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Original file line number Diff line number Diff line change
Expand Up @@ -3,21 +3,14 @@
const {
Array,
ArrayIsArray,
BigInt64Array,
BigIntPrototypeValueOf,
BigUint64Array,
BooleanPrototypeValueOf,
DatePrototypeGetTime,
DatePrototypeToISOString,
DatePrototypeToString,
ErrorPrototypeToString,
Float32Array,
Float64Array,
FunctionPrototypeCall,
FunctionPrototypeToString,
Int8Array,
Int16Array,
Int32Array,
JSONStringify,
Map,
MapPrototypeGetSize,
Expand Down Expand Up @@ -59,10 +52,8 @@ const {
SymbolIterator,
SymbolToStringTag,
TypedArrayPrototypeGetLength,
Uint16Array,
Uint32Array,
TypedArrayPrototypeGetSymbolToStringTag,
Uint8Array,
Uint8ClampedArray,
uncurryThis,
} = primordials;

Expand Down Expand Up @@ -120,17 +111,6 @@ const {
isNumberObject,
isBooleanObject,
isBigIntObject,
isUint8Array,
isUint8ClampedArray,
isUint16Array,
isUint32Array,
isInt8Array,
isInt16Array,
isInt32Array,
isFloat32Array,
isFloat64Array,
isBigInt64Array,
isBigUint64Array
} = require('internal/util/types');

const assert = require('internal/assert');
Expand Down Expand Up @@ -712,26 +692,6 @@ function formatProxy(ctx, proxy, recurseTimes) {
ctx, res, '', ['Proxy [', ']'], kArrayExtrasType, recurseTimes);
}

function findTypedConstructor(value) {
for (const [check, clazz] of [
[isUint8Array, Uint8Array],
[isUint8ClampedArray, Uint8ClampedArray],
[isUint16Array, Uint16Array],
[isUint32Array, Uint32Array],
[isInt8Array, Int8Array],
[isInt16Array, Int16Array],
[isInt32Array, Int32Array],
[isFloat32Array, Float32Array],
[isFloat64Array, Float64Array],
[isBigInt64Array, BigInt64Array],
[isBigUint64Array, BigUint64Array]
]) {
if (check(value)) {
return clazz;
}
}
}

// Note: using `formatValue` directly requires the indentation level to be
// corrected by setting `ctx.indentationLvL += diff` and then to decrease the
// value afterwards again.
Expand Down Expand Up @@ -879,10 +839,9 @@ function formatRaw(ctx, value, recurseTimes, typedArray) {
let bound = value;
let fallback = '';
if (constructor === null) {
const constr = findTypedConstructor(value);
fallback = constr.name;
fallback = TypedArrayPrototypeGetSymbolToStringTag(value);
Comment on lines 840 to +842
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This should probably use:

Suggested change
let fallback = '';
if (constructor === null) {
const constr = findTypedConstructor(value);
fallback = constr.name;
fallback = TypedArrayPrototypeGetSymbolToStringTag(value);
const fallback = TypedArrayPrototypeGetSymbolToStringTag(value);
if (constructor === null) {

So that fallback is always non‑empty.

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I think the idea originally was to avoid the overhead of a function call where possible. Judging from our test coverage stats, constructor being null is the unusual case (616 times hitting the if but only 33 times evaluating to true).

The performance difference seems likely to be unmeasurable and the code simplification may very well be worth it. But I'd prefer that be handled in a separate pull request. I'd prefer that this pull request preserve the code shape and merely replace/eliminate the existing function.

This is reminding me to run benchmarks for this change.

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@ExE-Boss ExE-Boss Dec 10, 2020 •
edited
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Well, TypedArrayPrototypeGetSymbolToStringTag is already invoked by isTypedArray:

node/lib/internal/util/types.js

Lines 8 to 10 in 72b07e4

function isTypedArray(value) {
return TypedArrayPrototypeGetSymbolToStringTag(value) !== undefined;
}

It should be possible to reduce this to always perform only one TypedArrayPrototypeGetSymbolToStringTag call, even in the constructor === null case, but that is probably overkill:

   if (value[SymbolIterator] || constructor === null) {
     noIterator = false;
+    let typedArrayName;
     if (ArrayIsArray(value)) {
-    } else if (isTypedArray(name)) {
+    } else if ((typedArrayName = TypedArrayPrototypeGetSymbolToStringTag(value)) !== undefined) {
       keys = getOwnNonIndexProperties(value, filter);
       let bound = value;
-      let fallback = '';
       if (constructor === null) {
-        fallback = TypedArrayPrototypeGetSymbolToStringTag(value);
         // Reconstruct the array information.
-        bound = new primordials[primordials](value);
+        bound = new primordials[typedArrayName](value);
       }
       const size = TypedArrayPrototypeGetLength(value);
-      const prefix = getPrefix(constructor, tag, fallback, `(${size})`);
+      const prefix = getPrefix(constructor, tag, typedArrayName, `(${size})`);

// Reconstruct the array information.
bound = new constr(value);
bound = new primordials[fallback](value);
}
const size = TypedArrayPrototypeGetLength(value);
const prefix = getPrefix(constructor, tag, fallback, `(${size})`);
Expand Down