JavaScript for...in: Enumerate Properties and Guard Own Keys

The task

Inspect a small status record with an inherited category and a hidden note. Collect keys first, then collect only own keys using a guard.

Runnable Node 22 example

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

const report = Object.create({category: 'inventory'});
report.open = 2;
Object.defineProperty(report, 'privateNote', {value: 'draft', enumerable: false});
const all = [];
const own = [];
for (const key in report) {
  all.push(key);
  if (Object.hasOwn(report, key)) own.push(key);
}
assert.deepEqual(all.sort(), ['category', 'open']);
assert.deepEqual(own, ['open']);
const values = [];
for (const value of ['east', 'west']) values.push(value);
assert.deepEqual(values, ['east', 'west']);
console.log(`all=${all.join(',')}; own=${own.join(',')}`);

Expected output and explanation

The inherited category appears in the unguarded key list, while the non-enumerable privateNote does not. The own-property guard retains only open. The sort is used to make the diagnostic comparison independent of the collection order this task does not need.

The separate for...of loop demonstrates value iteration on an array. Using for...in there would produce keys rather than the east and west strings. Choose the loop from the structure and the values the body actually needs.

Pitfall to check

Do not mutate a prototype chain during enumeration and assume a simple static key list. This fixture keeps the object stable. If a fixed own-key snapshot is the requirement, Object.keys followed by a loop may express it more directly.