noUselessTernary

import { Tabs, TabItem } from '@astrojs/starlight/components';

<Tabs> <TabItem label="JavaScript (and super languages)" icon="seti:javascript"> ## Summary - Rule available since: `v1.5.0` - Diagnostic Category: [`lint/complexity/noUselessTernary`](/reference/diagnostics#diagnostic-category) - This rule is **recommended**, meaning it is enabled by default. - This rule has an [**unsafe**](/linter/#unsafe-fixes) fix. - The default severity of this rule is [**information**](/reference/diagnostics#information). - Sources: - Same as [`no-unneeded-ternary`](https://eslint.org/docs/latest/rules/no-unneeded-ternary)

How to configure

json

{
	"linter": {
		"rules": {
			"complexity": {
				"noUselessTernary": "error"
			}
		}
	}
}

Description

Disallow ternary operators when simpler alternatives exist.

It’s a common mistake in JavaScript to use a conditional expression to select between two boolean values instead of using the logical NOT (!) or double NOT (!!) to convert the test to a boolean.

Examples

Invalid

var a = x ? true : true;

var a = foo === 1 ? false : true;

<pre class="language-text"><code class="language-text">code-block.js:1:9 <a href="https://biomejs.dev/linter/rules/no-useless-ternary">lint/complexity/noUselessTernary</a> FIXABLE ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ ℹ Unnecessary use of boolean literals in conditional expression. > 1 │ var a = foo === 1 ? false : true; │ ^^^^^^^^^^^^^^^^^^^^^^^^ 2 │ ℹ Simplify your code by directly assigning the result without using a ternary operator. ℹ If your goal is negation, you may use the logical NOT (!) or double NOT (!!) operator for clearer and concise code. Check for more details about <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Logical_NOT">NOT</a> operator. ℹ Unsafe fix: Remove the conditional expression with 1 │ - var·a·=·foo·===·1·?·false·:·true; 1 │ + var·a·=·foo·!==1; 2 2 │ </code></pre>

var a = foo + 1 ? false : true;

<pre class="language-text"><code class="language-text">code-block.js:1:9 <a href="https://biomejs.dev/linter/rules/no-useless-ternary">lint/complexity/noUselessTernary</a> FIXABLE ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ ℹ Unnecessary use of boolean literals in conditional expression. > 1 │ var a = foo + 1 ? false : true; │ ^^^^^^^^^^^^^^^^^^^^^^ 2 │ ℹ Simplify your code by directly assigning the result without using a ternary operator. ℹ If your goal is negation, you may use the logical NOT (!) or double NOT (!!) operator for clearer and concise code. Check for more details about <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Logical_NOT">NOT</a> operator. ℹ Unsafe fix: Remove the conditional expression with 1 │ - var·a·=·foo·+·1·?·false·:·true; 1 │ + var·a·=·!(foo·+·1·); 2 2 │ </code></pre>

var a = foo + 1 ? true : false;

<pre class="language-text"><code class="language-text">code-block.js:1:9 <a href="https://biomejs.dev/linter/rules/no-useless-ternary">lint/complexity/noUselessTernary</a> FIXABLE ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ ℹ Unnecessary use of boolean literals in conditional expression. > 1 │ var a = foo + 1 ? true : false; │ ^^^^^^^^^^^^^^^^^^^^^^ 2 │ ℹ Simplify your code by directly assigning the result without using a ternary operator. ℹ If your goal is negation, you may use the logical NOT (!) or double NOT (!!) operator for clearer and concise code. Check for more details about <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Logical_NOT">NOT</a> operator. ℹ Unsafe fix: Remove the conditional expression with 1 │ - var·a·=·foo·+·1·?·true·:·false; 1 │ + var·a·=·!!(foo·+·1·); 2 2 │ </code></pre>

Valid

var a = x === 2 ? 'Yes' : 'No';

var a = x === 2 ? 'Yes' : false;

Resources

Logical NOT: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Logical_NOT

</TabItem> </Tabs>