#no-useless-fallback-in-spread

#Configuration

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

export default defineConfig([
  unicornPlugin.configs.recommended,
  {
    rules: {
      'unicorn/no-useless-fallback-in-spread': 'error',
    },
  },
]);

#Rule Details

Disallow an empty object fallback in an object spread. Spreading undefined, null, or another falsy value into an object adds no properties, so the fallback is unnecessary.

Examples of incorrect code:

const object = { ...(foo || {}) };
const other = { ...(foo ?? {}) };

Examples of correct code:

const object = { ...foo };
const conditional = { ...(foo && {}) };
const array = [...(foo || [])];

#Automatic Fixes

Fixes preserve the left operand and its comments. When removing the fallback would delete a comment, the rule reports the empty object without offering a fix.

Like upstream, this rule assumes falsy values have no enumerable properties. Browser code that may spread document.all should disable the rule for that expression: document.all is falsy but can have enumerable properties, so removing its fallback can change the result.

#Options

This rule has no options.

#Differences from upstream

Fixes keep the parentheses required by JavaScript JSDoc @type assertions:

const object = {.../** @type {object} */ (value || {})};
// Fixed:
const object = {.../** @type {object} */ (value)};

This preserves the assertion when checkJs or // @ts-check is enabled. Unicorn v79.0.0 removes these parentheses, which can introduce a spread-type error when value has type unknown.

#Original Documentation

• eslint-plugin-unicorn: no-useless-fallback-in-spread
• Source code