mongodb/node-mongodb-native · warning · MongoParseError

Cannot make WriteConcern from wtimeout

Error message

Cannot make WriteConcern from wtimeout

What it means

`wtimeout` is a deprecated write-concern option (descriptor: `deprecated: 'Please use wtimeoutMS instead'`). The transform at src/connection_string.ts:1208 builds a WriteConcern from `{...options.writeConcern, wtimeout: getUIntFromOptions('wtimeout', value)}`; if fromOptions returns falsy, MongoParseError is thrown at src/connection_string.ts:1216. Non-uint values fail earlier inside getUIntFromOptions.

Solutions

1. Use `wtimeoutMS` (the canonical name) instead of `wtimeout`.
2. Pair it with a valid `w`, e.g. `writeConcern: { w: 'majority', wtimeoutMS: 1000 }`.
3. Audit config merging so `w` is not deleted alongside wtimeout.

Example fix

// before
new MongoClient(uri, { wtimeout: 1000 });

// after
new MongoClient(uri, { writeConcern: { w: 'majority', wtimeoutMS: 1000 } });

if ('wtimeout' in (opts as any)) {
  console.warn('wtimeout is deprecated; use wtimeoutMS');
  const ms = Number((opts as any).wtimeout);
  delete (opts as any).wtimeout;
  opts.writeConcern = { ...(opts.writeConcern as any), wtimeoutMS: ms };
}

null

try { client = new MongoClient(uri, opts); } catch (e) { if (e instanceof MongoParseError && /wtimeout/.test(e.message)) { const ms = (opts as any).wtimeout; delete (opts as any).wtimeout; opts.writeConcern = { w: 'majority', wtimeoutMS: ms }; client = new MongoClient(uri, opts); } else throw e; }

When it happens

Trigger: Passing `wtimeout: 1000` while the surrounding writeConcern fields leave fromOptions with nothing valid to build; layering `wtimeout` over a writeConcern object whose `w` field was removed.

Common situations: Carrying forward v3-era option names; config merge layers that strip `w`; using wtimeout without also specifying a replication factor.

Understand the failure class

• Timeouts: ETIMEDOUT, deadlines, and hung requests — what actually expires when a request times out.

Related errors

• Unable to make a writeConcern from fsync=
• Unable to make a writeConcern from journal=
• Invalid WriteConcern cannot parse
• Argument "iterator" must be a function
• Auth mechanism property ALLOWED_HOSTS must be an array of…

AI-assisted analysis of mongodb/node-mongodb-native@dce7939f86 (2026-08-11). Data as JSON: /api/errors/96e7c2d537f746b5. Report an issue: GitHub.

Appendix: source

Thrown at src/connection_string.ts:1216

          }
        });
      }

      throw new MongoParseError(`Invalid WriteConcern cannot parse: ${JSON.stringify(value)}`);
    }
  },
  wtimeout: {
    deprecated: 'Please use wtimeoutMS instead',
    target: 'writeConcern',
    transform({ values: [value], options }) {
      const wc = WriteConcern.fromOptions({
        writeConcern: {
          ...options.writeConcern,
          wtimeout: getUIntFromOptions('wtimeout', value)
        }
      });
      if (wc) return wc;
      throw new MongoParseError(`Cannot make WriteConcern from wtimeout`);
    }
  } as OptionDescriptor,
  wtimeoutMS: {
    target: 'writeConcern',
    transform({ values: [value], options }) {
      const wc = WriteConcern.fromOptions({
        writeConcern: {
          ...options.writeConcern,
          wtimeoutMS: getUIntFromOptions('wtimeoutMS', value)
        }
      });
      if (wc) return wc;
      throw new MongoParseError(`Cannot make WriteConcern from wtimeout`);
    }
  },
  zlibCompressionLevel: {
    default: 0,
    type: 'int'

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