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feat(NODE-4793): add Symbol.toStringTag to all BSON types #880

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feat(NODE-4793): add Symbol.toStringTag to all BSON types #880

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3 changes: 3 additions & 0 deletions src/bson_value.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -29,6 +29,9 @@ export abstract class BSONValue {
public get [bsonType](): this['_bsontype'] {
return this._bsontype;
}
public get [Symbol.toStringTag](): string {
return this._bsontype;
}

/** @internal */
get [BSON_VERSION_SYMBOL](): typeof BSON_MAJOR_VERSION {
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11 changes: 11 additions & 0 deletions test/node/bson_type_classes.test.ts
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Expand Up @@ -98,6 +98,17 @@ describe('BSON Type classes common interfaces', () => {
));
}

if (TypeClass.name !== 'UUID') {
it(`defines Symbol.toStringTag equal to its name`, () =>
expect(TypeClass.prototype).to.have.property(Symbol.toStringTag, TypeClass.name));
} else {
it(`UUID inherits Symbol.toStringTag from Binary`, () =>
expect(Object.getPrototypeOf(TypeClass.prototype)).to.have.property(
Symbol.toStringTag,
'Binary'
));
Comment on lines +105 to +109
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@tadjik1 tadjik1 Apr 21, 2026

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Approach is right - matches the existing bsonType getter pattern on BSONValue. One suggestion: override Symbol.toStringTag on UUID to return 'UUID'. _bsontype is a wire-protocol key and must stay 'Binary' (serializer dispatches on it), but Symbol.toStringTag is a developer-facing identity hint with no wire impact - making it reflect the JS class gives nicer debug output ([object UUID]) without breaking anything. The test would then assert toStringTag === TypeClass.name uniformly across all types.

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@nbbeeken nbbeeken Apr 21, 2026 •
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> Object.prototype.toString.call(Buffer.alloc(0))
'[object Uint8Array]'

It is not always the case that the string tag matches the class name, because UUID is a trivial subclass of Binary and Binary is the relevant BSON type it may make sense to keep these matching the _bsontype field. It also is not only a developer hint here's an example where it's a load bearing type check.

An additional benefit to adding this field is it adds the same functionality we added when we introduced the @@mdb.bson.type symbol but without the need to import/create something from the library.

Just my opinion here :) not strongly held

}

it(`defines a Symbol.for('@@mdb.bson.version') property equal to 7`, () =>
expect(TypeClass.prototype).to.have.property(Symbol.for('@@mdb.bson.version'), 7));

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