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inspect: fix console.log(%s, { [Symbol.toPrimitive]: () => hello }) #50992

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May 12, 2024
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inspect: fix console.log(%s, { [Symbol.toPrimitive]: () => hello }) #50992

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6 changes: 6 additions & 0 deletions lib/internal/util/inspect.js
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Original file line number Diff line number Diff line change
Expand Up @@ -87,6 +87,7 @@ const {
SymbolIterator,
SymbolPrototypeToString,
SymbolPrototypeValueOf,
SymbolToPrimitive,
SymbolToStringTag,
TypedArrayPrototypeGetLength,
TypedArrayPrototypeGetSymbolToStringTag,
Expand Down Expand Up @@ -2103,6 +2104,11 @@ function hasBuiltInToString(value) {
value = proxyTarget;
}

// Check if value has a custom Symbol.toPrimitive transformation.
if (typeof value[SymbolToPrimitive] === 'function') {
return false;
}

// Count objects that have no `toString` function as built-in.
if (typeof value.toString !== 'function') {
return true;
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21 changes: 21 additions & 0 deletions test/parallel/test-util-format.js
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Original file line number Diff line number Diff line change
Expand Up @@ -269,6 +269,27 @@ assert.strictEqual(util.format('%s', -Infinity), '-Infinity');
);
}

// Symbol.toPrimitive handling for string format specifier
{
const objectWithToPrimitive = {
[Symbol.toPrimitive](hint) {
switch (hint) {
case 'number':
return 42;
case 'string':
return 'string representation';
case 'default':
default:
return 'default context';
}
}
};

assert.strictEqual(util.format('%s', +objectWithToPrimitive), '42');
assert.strictEqual(util.format('%s', objectWithToPrimitive), 'string representation');
assert.strictEqual(util.format('%s', objectWithToPrimitive + ''), 'default context');
}

// JSON format specifier
assert.strictEqual(util.format('%j'), '%j');
assert.strictEqual(util.format('%j', 42), '42');
Expand Down