Safe Own-Property Lookups

When you look up values in plain objects using strings derived from user input (e.g., file paths, names, extensions), only accept own properties. Use Object.hasOwn(...) (or Object.prototype.hasOwnProperty.call) so special/inherited keys like __proto__, constructor, and toString can’t influence results.

Apply this rule to any “dictionary” object (e.g., Record<string, ...>) used for security-sensitive behavior or rendering decisions.

Example:

type IconSpec = { /* ... */ };
const BY_EXTENSION: Record<string, IconSpec> = {
  ts: { /* ... */ },
  json: { /* ... */ },
};

function lookupByExtension(ext: string): IconSpec | null {
  // ext may come from a user-controlled filename/path
  if (Object.hasOwn(BY_EXTENSION, ext)) {
    return BY_EXTENSION[ext];
  }
  return null; // safe default
}

Coding standard:

• Prefer Object.hasOwn(map, key) before reading map[key].
• Otherwise fall back to a safe neutral default.
• Add tests for keys like __proto__, constructor, and toString where applicable.