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defaults ​

Problem ​

You have a config object with some optional fields and need to fill in missing values from a set of fallbacks without overwriting explicitly-set values.

Solution ​

Use defaults(target, ...sources) to apply source values only where the target key is undefined.

ts
import { defaults } from '@vielzeug/arsenal';

const config = { host: 'localhost', port: undefined, secure: undefined };
const result = defaults(config, { port: 3000, secure: false, retries: 3 });
// { host: 'localhost', port: 3000, secure: false, retries: 3 }

Pitfalls ​

  • Only fills in undefined values — null and false are left unchanged.
  • Does not deep-merge nested objects; use deepMerge for recursive defaults.