@lint-suite/eslint-plugin-ternary-branch-shape

This ESLint rule for TypeScript keeps JavaScript and TypeScript ternaries readable by requiring each branch to be a name, literal, template literal, unary literal, or plain member access. Use it when a ternary would otherwise combine selection with computation.

Compatibility

Requires ESLint ^10.9.1 and TypeScript >=6.0.3. The package is built and tested with Node.js 24.

Installation

pnpm add -D @lint-suite/eslint-plugin-ternary-branch-shape eslint@^10.9.1 typescript@^6.0.3 typescript-eslint@^8.69.0

Configuration

The plugin does not configure a parser. This flat config parses the TypeScript examples below:

import plugin from '@lint-suite/eslint-plugin-ternary-branch-shape';
import tseslint from 'typescript-eslint';

export default [
  {
    files: ['**/*.ts'],
    languageOptions: { parser: tseslint.parser },
    plugins: { 'ternary-branch-shape': plugin },
    rules: { 'ternary-branch-shape/ternary-branch-shape': 'error' }
  }
];

Options

This rule has no options.

Examples

Each snippet is checked by ternary-branch-shape alone with its default configuration.

Valid examples

1. Select between identifiers

const result = enabled ? primary : fallback;

Both branches are names.

2. Select between literals

const result = enabled ? 1 : 'fallback';

Literal branches are allowed.

3. Return a template literal branch

const label = enabled ? `enabled` : fallback;

Template literals are allowed.

4. Select a plain member chain

const label = enabled ? user.profile.label : fallback;

The member chain does not begin with a call.

5. Use a unary literal

const direction = descending ? -1 : 1;

A unary expression over a literal is allowed.

Invalid examples

1. Call a function in the consequent

const result = enabled ? createResult() : fallback;

The consequent branch is a call expression.

2. Calculate in the alternate

const result = enabled ? primary : fallback + suffix;

The alternate branch is a binary expression.

3. Use a member chain that starts from a call

const result = enabled ? service.create().label : fallback;

Plain member access cannot have a call in its object chain.

4. Negate a named value

const result = enabled ? -score : fallback;

Only unary expressions over literals are allowed.

5. Construct an object in a branch

const result = enabled ? { enabled: true } : fallback;

The object expression should be named before the ternary.

The rule checks both branches of every ternary expression; it does not restrict the condition. The named ternaryBranchShapeRule export is for composed plugin registries.