feat(isDate, isRegExp): support cross-realm

[haejunejung]

Support cross-realm

Problem

instanceof fails when checking objects created in different JavaScript realms (e.g., iframes, vm contexts). Each realm has its own set of built-in constructors, so value instanceof RegExp returns false for a RegExp created in another realm.

const vm = require('node:vm');
const context = vm.createContext({});
const regex = vm.runInContext('/test/', context);

regex instanceof RegExp;  // false
Object.prototype.toString.call(regex) === '[object RegExp]';  // true

date instanceof Date; // false
Object.prototype.toString.call(date) === '[object Date]'; // true

Solution

Replace instanceof with Object.prototype.toString.call(), which checks the object's internal [[Class]] slot and works reliably across realms.

Changes

• Changed type checking to use Object.prototype.toString.call() instead of instanceof
• Added cross-realm tests using node:vm

Reference

• MDN - instanceof and multiple realms

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Project	Deployment	Review	Updated (UTC)
es-toolkit	Ready	Preview, Comment	Jan 2, 2026 1:58pm

[Copilot]

Pull request overview

This PR adds cross-realm support to isDate and isRegExp predicates by replacing instanceof checks with Object.prototype.toString.call(), which works reliably across different JavaScript realms (e.g., iframes, VM contexts).

Key Changes:

• Replaced instanceof checks with Object.prototype.toString.call() for realm-independent type checking
• Added isObject guard for performance optimization before the toString check
• Added cross-realm tests using node:vm module

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
src/predicate/isRegExp.ts	Updated implementation to use Object.prototype.toString.call() instead of instanceof RegExp
src/predicate/isRegExp.spec.ts	Added cross-realm test using runInNewContext
src/predicate/isDate.ts	Updated implementation to use Object.prototype.toString.call() instead of instanceof Date
src/predicate/isDate.spec.ts	Added cross-realm test using runInNewContext

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[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.97%. Comparing base (6d278b4) to head (7bc7002).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1568   +/-   ##
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  Coverage   99.97%   99.97%           
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  Files         495      495           
  Lines        4648     4648           
  Branches     1340     1342    +2     
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  Hits         4647     4647           
  Misses          1        1           

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[raon0211]

Hey, thanks for the PR! We're not sure cross-realm support is a common enough use case for us to prioritize. es-toolkit aims to keep implementations simple and cover ~85% of real-world scenarios—edge cases aren't really our focus (more on that in our contributing guide).

For checking RegExp or Date values, we think instanceof is the more straightforward approach, so we'll stick with what we have.

Appreciate the contribution though—hope to see more from you!