Flatten & Expand

flatten() and expand() are inverses. They convert between a nested object and a single-level object whose keys are notations.

Flatten

const obj = { car: { brand: 'Dodge', model: 'Charger', year: 1970 } };
Notation.create(obj).flatten().value;
// » {
//     "car.brand": "Dodge",
//     "car.model": "Charger",
//     "car.year": 1970
//   }

Expand

The opposite — nest dotted keys back under their parents. This is handy for flat rows coming out of a database or a form.

Take this flat row:

{
  "id": 42,
  "name": "Jane Doe",
  "account.plan": "pro",
  "account.billing.card.brand": "visa",
  "account.billing.card.last4": "4242",
  "profile.social.github": "jane"
}

import row from './flat-row.json' with { type: 'json' };

Notation.create(row).expand().value;
// » {
//     id: 42,
//     name: "Jane Doe",
//     account: {
//       plan: "pro",
//       billing: { card: { brand: "visa", last4: "4242" } }
//     },
//     profile: { social: { github: "jane" } }
//   }

Round-Trip

flatten() then expand() returns the original shape — useful for diffing, patching, or storing nested data in a flat column:

const data = { user: { name: 'Jane', roles: ['editor'] } };
const flat = Notation.create(data).flatten().value;
// » { "user.name": "Jane", "user.roles[0]": "editor" }

Notation.create(flat).expand().value;
// » { user: { name: "Jane", roles: ["editor"] } }