Create a Nested Object in JavaScript: Updates and Shared References

The task

Create a workspace configuration with export options, attach the options to another record and test an assignment through a missing intermediate path.

Runnable Node 22 example

const assert = require('node:assert/strict');

const config = {workspace: {export: {format: 'pdf'}}};
config.workspace.export.format = 'text';
const mirror = {options: config.workspace.export};
mirror.options.format = 'json';
assert.equal(config.workspace.export.format, 'json');
assert.throws(() => { config.delivery.email = true; }, TypeError);
config.delivery = {email: true};
assert.equal(config.delivery.email, true);
console.log(JSON.stringify(config));

Expected output and explanation

The first update reaches an existing nested export object. mirror then points to that same object, so its later update appears through config too. The relationship is intentional sharing, not a second independent configuration.

The delivery assignment fails before the intermediate object exists. Creating delivery with the intended shape makes the next check succeed. Optional chaining is useful for some reads, but it does not provide a general assignment mechanism that invents missing intermediate structures.

Pitfall to check

A shallow outer copy would still share existing child objects. If an update must be independent, duplicate the required nested structure deliberately and test the resulting references. Do not accept arbitrary property paths from external input without defining permitted fields.