object.filter'd objects fail strictEquals checks with normal object

If you filter an object, and try to strictEqual it with a POJO with the filtered fields, the assertion fails.

import {expect} from '@playwright/test'
import stdlib  from '@logdna/stdlib'

const o = {
    field: 'val'
    , field2: 'val2'
}

const e = {field: 'val'}
const f = stdlib.object.filter(o, (k) => k !== 'field2')

console.log(e)
console.log(f)

expect(e).toStrictEqual(f)

I'm not sure where playwright gets it's expect library from, and couldn't find out with a few minutes of searching.

> node fail.js
{ field: 'val' }
[Object: null prototype] { field: 'val' }
/Users/jmoses/dev/logdna/qa-e2e-pipeline/node_modules/@playwright/test/lib/matchers/expect.js:131
      if (!testInfo) return matcher.call(target, ...args);
                                    ^

Ze [Error]: expect(received).toStrictEqual(expected) // deep equality

Expected: {"field": "val"}
Received: serializes to the same string
    at Proxy.<anonymous> (/Users/jmoses/dev/logdna/qa-e2e-pipeline/node_modules/@playwright/test/lib/matchers/expect.js:131:37)
    at file:///Users/jmoses/dev/logdna/qa-e2e-pipeline/fail.js:15:11
    at ModuleJob.run (node:internal/modules/esm/module_job:198:25)
    at async Promise.all (index 0)
    at ESMLoader.import (node:internal/modules/esm/loader:385:24)
    at loadESM (node:internal/process/esm_loader:88:5)
    at handleMainPromise (node:internal/modules/run_main:61:12) {
  matcherResult: {
    actual: { field: 'val' },
    expected: [Object: null prototype] { field: 'val' },
    message: '\x1B[2mexpect(\x1B[22m\x1B[31mreceived\x1B[39m\x1B[2m).\x1B[22mtoStrictEqual\x1B[2m(\x1B[22m\x1B[32mexpected\x1B[39m\x1B[2m) // deep equality\x1B[22m\n' +
      '\n' +
      'Expected: \x1B[32m{"field": "val"}\x1B[39m\n' +
      'Received: serializes to the same string',
    name: 'toStrictEqual',
    pass: false
  }
}

> npm list | grep -E 'playwright/test|logdna/stdlib'
├── @logdna/stdlib@1.2.0
├── @playwright/test@1.32.1

Run the fail.js reproduction and inspect the implementation behind stdlib.object.filter, focusing on why its result differs from a normal object during strict equality checks. Done means the filtered result passes the shown toStrictEqual assertion against the equivalent POJO without changing the reported field values.