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Compatibility Contract — @stackline/deep-is

Project compatibility notes for @stackline/deep-is 1.0.6. Review behavior, requirements and limitations.

Versioned project notes for @stackline/deep-is 1.0.6. Original attribution is retained in the linked repository.

Compatibility Contract

Baseline: [email protected]

Public API

const deepIs = require('deep-is');
const same = deepIs(actual, expected);

The package exports one synchronous callable function. It returns a boolean and does not mutate either input.

Preserved Equality Semantics

  • Identical values compare equal except positive and negative zero differ.
  • NaN compares equal to NaN.
  • Two dates compare their millisecond timestamps.
  • Two non-object values fall back to loose == comparison.
  • Other pairs compare enumerable own string keys recursively.
  • Key order does not affect equality.
  • Arguments objects are converted to arrays before comparison.
  • The historical .prototype property check remains intact.
  • Symbol keys, non-enumerable keys, and modern Map/Set internals remain outside the baseline contract.

This intentionally preserves cases that differ from modern strict equality, including deepIs(1, '1') === true and legacy array/object equivalence.

Maintained Extension

  • Cyclic object graphs are processed without call-stack failure.
  • Deep acyclic graphs are processed iteratively without recursive stack exhaustion.
  • Revisited object pairs terminate deterministically. Reference alias topology is not treated as a new equality dimension, matching the old behavior for repeated acyclic references.

Errors

Exceptions raised by user-controlled getters, proxies, or coercion hooks remain observable where the baseline exposed them. The implementation does not hide arbitrary user-code errors. Native recursion RangeError is removed for normal object-graph traversal.

Modules And Types

  • CommonJS remains callable.
  • Native ESM provides a default export of the same function.
  • First-party TypeScript declarations use syntax compatible with TypeScript 3.9 and newer.
  • Browser builds preserve the same synchronous function.

Runtime Target

Node.js 12 and newer, plus current browser bundles. Development tooling may require a newer Node.js release and is not part of the runtime contract.

Package reference