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no-use-extend-native

Disallow usage of non-native members on built-in JavaScript objects.

Targeted pattern scope​

This rule is intentionally conservative and focuses on obvious built-in object shapes such as:

  • String/number/boolean/regexp literals.
  • Array/object literals.
  • new expressions for built-ins.
  • String.prototype.<member> / Array.prototype.<member> style accesses.

It does not attempt full-flow inference for arbitrary identifiers.

What this rule reports​

This rule helps prevent implicit reliance on monkey-patched native prototypes (for example from legacy libraries that add methods like String.prototype.green).

This rule reports member usage on obvious built-in values when the accessed member is not part of the native API.

Why this rule exists​

Relying on extended native objects can make code unpredictable across runtimes, bundling targets, and dependency versions.

❌ Incorrect​

const value = "unicorn".green;
const value = [].customFunction();
const value = String.prototype.shortHash();

✅ Correct​

const value = "unicorn".toUpperCase();
const value = [].map((entry) => entry);
const value = String.prototype.toLowerCase.call("ABC");

Behavior and migration notes​

This rule has no options.

Relationship to ESLint no-extend-native​

  • ESLint core no-extend-native prevents adding properties to native prototypes.
  • This rule prevents consuming non-native members when they appear in code.

Using both rules together gives better protection:

  1. Prevent introducing prototype extension.
  2. Prevent relying on prototype extension from third-party code.

Original plugin source: eslint-plugin-no-use-extend-native.

ESLint flat config example​

import etcMisc from "eslint-plugin-etc-misc";

export default [
 {
  plugins: { "etc-misc": etcMisc },
  rules: {
   "etc-misc/no-use-extend-native": "error",
  },
 },
];

When not to use it​

  • If your project intentionally and explicitly relies on controlled prototype extension.
  • If your runtime environment guarantees specific prototype patches and that dependency is accepted in your architecture.

Further reading​