defaults

Fills missing or nullish fields from a fallback object.

const withDefaults = defaults({role: 'viewer', verified: false});

withDefaults({name: 'Ada', role: null});
// {name: 'Ada', role: 'viewer', verified: false}

Only null and undefined trigger a fallback. Values such as false, 0, NaN, and '' remain unchanged.

Defaults are shallow and the input object is not mutated. When a field already has a non-nullish value, its inferred type is combined with the fallback type.