#prefer-ternary

#Configuration

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

export default defineConfig([
  unicornPlugin.configs.recommended,
  {
    rules: {
      'unicorn/prefer-ternary': 'error',
    },
  },
]);

#Rule Details

This rule flags simple if statements that return or assign a value and suggests replacing them with a ternary expression. A separate branch collapses let x = a; if (test) { x = b; } into a single const x = test ? b : a; declaration (or let x = … when the variable gets a later write).

The motivation is that if-else statements typically produce more lines than a ternary, leading to a larger, harder-to-maintain codebase. They can also force developers to use let or var for variables that only get reassigned, which unnecessarily introduces mutability and blocks prefer-const from flagging the variable.

Examples of incorrect code for this rule:

function unicorn() {
    if (test) {
        return a;
    } else {
        return b;
    }
}

let foo;
if (test) {
    foo = 1;
} else {
    foo = 2;
}

Examples of correct code for this rule:

function unicorn() {
    return test ? a : b;
}

const foo = test ? 1 : 2;

#Options

Type: string

Default: 'always'

• 'always' (default) — Always report supported IfStatement returns and assignments where a ternary can be used.
• 'only-single-line' — Only report when the condition and the merged expressions fit on a single line.

Example with 'only-single-line':

// Not flagged — array literal spans multiple lines.
if (test) {
    foo = [
        'multiple line array'
    ];
} else {
    foo = bar;
}

#Differences from ESLint

The upstream unicorn/prefer-ternary rule is reported under eslint-plugin-unicorn's recommended and unopinionated configs and auto-fixes via --fix. The current port reproduces that contract:

• The simple if/else form is rewritten to a ternary and the result is reported with a single diagnostic whose fix rewrites the source.
• The let x = a; if (test) x = b; form is reported with a diagnostic whose suggest rewrites the source to const x = test ? b : a; (or let when the variable receives a later write).

#Original Documentation

• eslint-plugin-unicorn: prefer-ternary
• Source code