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deepMerge / shallowMerge ​

Problem ​

You need to combine configuration objects without stomping nested values.

Solution ​

Pass deep-merge sources as an array. Configuration stays separate from data. Use shallowMerge(...items) for a single-level Object.assign-style merge.

ts
import { deepMerge } from '@vielzeug/arsenal/object';

const base = { api: { host: 'localhost', port: 3000 }, retries: 3 };
const overrides = { api: { port: 4000 }, timeout: 5_000 };

const merged = deepMerge([base, overrides]);
// { api: { host: 'localhost', port: 4000 }, retries: 3, timeout: 5_000 }

Concatenate arrays instead of replacing them ​

ts
import { deepMerge } from '@vielzeug/arsenal/object';

const merged = deepMerge([{ tags: ['ts', 'node'] }, { tags: ['vue'] }], { arrayStrategy: 'concat' });
// { tags: ['ts', 'node', 'vue'] }

Pitfalls ​

  • deepMerge replaces arrays by default.
  • Options are second argument; source objects always stay in first array argument.
  • Later sources win on key conflicts.