useDefaultParameterLast

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

<Tabs> <TabItem label="JavaScript (and super languages)" icon="seti:javascript"> ## Summary - Rule available since: `v1.0.0` - Diagnostic Category: [`lint/style/useDefaultParameterLast`](/reference/diagnostics#diagnostic-category) - This rule isn't recommended, so you need to enable it. - This rule has an [**unsafe**](/linter/#unsafe-fixes) fix. - The default severity of this rule is [**warning**](/reference/diagnostics#warning). - Sources: - Same as [`default-param-last`](https://eslint.org/docs/latest/rules/default-param-last) - Same as [`@typescript-eslint/default-param-last`](https://typescript-eslint.io/rules/default-param-last)

How to configure

json

{
	"linter": {
		"rules": {
			"style": {
				"useDefaultParameterLast": "error"
			}
		}
	}
}

Description

Enforce default function parameters and optional function parameters to be last.

Default and optional parameters that precede a required parameter cannot be omitted at call site.

Examples

Invalid

function f(a = 0, b) {}

<pre class="language-text"><code class="language-text">code-block.js:1:12 <a href="https://biomejs.dev/linter/rules/use-default-parameter-last">lint/style/useDefaultParameterLast</a> FIXABLE ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ ⚠ This default parameter should follow the last required parameter or should be a required parameter. > 1 │ function f(a = 0, b) {} │ ^^^^^ 2 │ ℹ The last required parameter is here: > 1 │ function f(a = 0, b) {} │ ^ 2 │ ℹ A default parameter that precedes a required parameter cannot be omitted at call site. ℹ Unsafe fix: Turn the parameter into a required parameter. 1 │ function·f(a·=·0,·b)·{} │ ---- </code></pre>

function f(a, b = 0, c) {}

<pre class="language-text"><code class="language-text">code-block.js:1:15 <a href="https://biomejs.dev/linter/rules/use-default-parameter-last">lint/style/useDefaultParameterLast</a> FIXABLE ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ ⚠ This default parameter should follow the last required parameter or should be a required parameter. > 1 │ function f(a, b = 0, c) {} │ ^^^^^ 2 │ ℹ The last required parameter is here: > 1 │ function f(a, b = 0, c) {} │ ^ 2 │ ℹ A default parameter that precedes a required parameter cannot be omitted at call site. ℹ Unsafe fix: Turn the parameter into a required parameter. 1 │ function·f(a,·b·=·0,·c)·{} │ ---- </code></pre>

function f(a: number, b?: number, c: number) {}

<pre class="language-text"><code class="language-text">code-block.ts:1:23 <a href="https://biomejs.dev/linter/rules/use-default-parameter-last">lint/style/useDefaultParameterLast</a> FIXABLE ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ ⚠ This optional parameter should follow the last required parameter or should be a required parameter. > 1 │ function f(a: number, b?: number, c: number) {} │ ^^^^^^^^^^ 2 │ ℹ The last required parameter is here: > 1 │ function f(a: number, b?: number, c: number) {} │ ^^^^^^^^^ 2 │ ℹ A optional parameter that precedes a required parameter cannot be omitted at call site. ℹ Unsafe fix: Turn the parameter into a required parameter. 1 │ function·f(a:·number,·b?:·number,·c:·number)·{} │ - </code></pre>

class Foo {
    constructor(readonly a = 10, readonly b: number) {}
}

<pre class="language-text"><code class="language-text">code-block.ts:2:17 <a href="https://biomejs.dev/linter/rules/use-default-parameter-last">lint/style/useDefaultParameterLast</a> FIXABLE ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ ⚠ This default parameter should follow the last required parameter or should be a required parameter. 1 │ class Foo { > 2 │ constructor(readonly a = 10, readonly b: number) {} │ ^^^^^^^^^^^^^^^ 3 │ } 4 │ ℹ The last required parameter is here: 1 │ class Foo { > 2 │ constructor(readonly a = 10, readonly b: number) {} │ ^^^^^^^^^^^^^^^^^^ 3 │ } 4 │ ℹ A default parameter that precedes a required parameter cannot be omitted at call site. ℹ Unsafe fix: Turn the parameter into a required parameter. 2 │ ····constructor(readonly·a·=·10,·readonly·b:·number)·{} │ ----- </code></pre>

Valid

function f(a, b = 0) {}

function f(a: number, b?: number, c = 0) {}

function f(a: number, b = 0, c?: number) {}

</TabItem> </Tabs>

How to configure

Description

Examples

Invalid

Valid

Related links