no-extend-native

A property added to Array.prototype or Object.prototype shows up on every array or object in the program, including the ones inside libraries. It appears in their for...in loops, and it breaks when a library or a later version of JavaScript defines the same name with a different meaning.

Both plain assignment and Object.defineProperty() / Object.defineProperties() are reported.

Configure

Off by default. To turn it on:

[lint.rules]
"no-extend-native" = "error" # or "warn"

Every option, set to its default:

[lint.rules]
"no-extend-native" = ["error", {
  exceptions = [], # list of strings
}]

Examples

Reported:

Array.prototype.last = function () {
  return this[this.length - 1];
};

Object.defineProperty(String.prototype, "shout", {
  value() {
    return this.toUpperCase() + "!";
  },
});

Not reported:

function last(items) {
  return items[items.length - 1];
}

class Stack extends Array {
  last() {
    return this[this.length - 1];
  }
}

Stack.prototype.peek = Stack.prototype.last;

Options

Option	Default	What it does
exceptions	[]	Names of built-in objects that you can extend.

Array.prototype.last = function () {
  return this[this.length - 1];
};

String.prototype.shout = function () {
  return this.toUpperCase() + "!";
};

When not to use it

A polyfill needs to add to built-in prototypes. List what it extends in exceptions, or turn the rule off for that file.