fix: Use globalThis to prevent environment check code from being re…

[xiaweiss]

fix #42

When bundling with Rolldown or tsdown, enabling code minification (compression) or tree-shaking (pruning) will cause the environment check code to be removed.

Works fine with esbuild and Rollup, they won’t remove it.

Before bundling

var envFlags = {
  flagGroups: (() => {
    try {
      new RegExp("(?i:)");
    } catch {
      return false;
    }
    return true;
  })(),
  unicodeSets: (() => {
    try {
      new RegExp("[[]]", "v");
    } catch {
      return false;
    }
    return true;
  })()
};

After bundling

var envFlags = {
  flagGroups: true,
  unicodeSets: true
};

Replacing RegExp with globalThis.RegExp can prevent this behavior.

[Copilot]

Pull request overview

Fixes incorrect tree-shaking/minification by some bundlers (Rolldown/tsdown) that were removing runtime RegExp feature-detection logic, which could cause envFlags to be incorrectly constant-folded.

Changes:

• Switched RegExp feature checks to use globalThis.RegExp to avoid bundler removal/constant-folding.
• Added an inline note explaining the bundler-related rationale.

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