#no-param-reassign

#Configuration

import { defineConfig, js } from '@rslint/core';

export default defineConfig([
  js.configs.recommended,
  {
    rules: {
      'no-param-reassign': 'error',
    },
  },
]);

#Rule Details

Disallow reassigning function parameters. Reassigning a parameter mutates the caller-visible arguments object in non-strict code and can hide bugs caused by unintentional overwrites. With the props option, the rule also forbids modifying properties on parameters.

Examples of incorrect code for this rule:

function foo(bar) {
  bar = 13;
}

function foo(bar) {
  bar++;
}

function foo(bar) {
  for (bar in baz) {
  }
}

Examples of correct code for this rule:

function foo(bar) {
  var baz = bar;
}

#Options

{ "no-param-reassign": ["error", { "props": false }] }

{
  "no-param-reassign": [
    "error",
    {
      "props": true,
      "ignorePropertyModificationsFor": ["acc", "e"],
      "ignorePropertyModificationsForRegex": ["^ctx"]
    }
  ]
}

• props (default false) — when true, assignments to properties of a parameter (e.g. bar.x = 0, delete bar.x, ++bar.x) are also reported.
• ignorePropertyModificationsFor (requires props: true) — parameter names for which property modifications are allowed.
• ignorePropertyModificationsForRegex (requires props: true) — regular expressions matching parameter names for which property modifications are allowed.

Examples of incorrect code with { "props": true }:

{ "no-param-reassign": ["error", { "props": true }] }

function foo(bar) {
  bar.prop = 'value';
}

function foo(bar) {
  delete bar.aaa;
}

function foo(bar) {
  bar.aaa++;
}

Examples of correct code with { "props": true, "ignorePropertyModificationsFor": ["bar"] }:

{
  "no-param-reassign": [
    "error",
    { "props": true, "ignorePropertyModificationsFor": ["bar"] }
  ]
}

function foo(bar) {
  bar.prop = 'value';
}

#Original Documentation

• ESLint no-param-reassign