noInnerDeclarations

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/correctness/noInnerDeclarations`](/reference/diagnostics#diagnostic-category) - This rule is **recommended**, meaning it is enabled by default. - This rule doesn't have a fix. - The default severity of this rule is [**error**](/reference/diagnostics#error). - Sources: - Same as [`no-inner-declarations`](https://eslint.org/docs/latest/rules/no-inner-declarations)

How to configure

json

{
	"linter": {
		"rules": {
			"correctness": {
				"noInnerDeclarations": "error"
			}
		}
	}
}

Description

Disallow function and var declarations that are accessible outside their block.

A var is accessible in the whole body of the nearest root (function, module, script, static block). To avoid confusion, they should be declared to the nearest root.

Prior to ES2015, function declarations were only allowed in the nearest root, though parsers sometimes erroneously accept them elsewhere. In ES2015, inside an ES module, a function declaration is always block-scoped.

Note that const and let declarations are block-scoped, and therefore they are not affected by this rule. Moreover, function declarations in nested blocks are allowed inside ES modules.

Examples

Invalid

cjs

if (test) {
    function f() {}
}

<pre class="language-text"><code class="language-text">code-block.cjs:2:5 <a href="https://biomejs.dev/linter/rules/no-inner-declarations">lint/correctness/noInnerDeclarations</a> ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ ✖ This function should be declared at the root of the script. 1 │ if (test) { > 2 │ function f() {} │ ^^^^^^^^^^^^^^^ 3 │ } 4 │ ℹ The function is accessible in the whole body of the script. To avoid confusion, it should be declared at the root of the script. </code></pre>

if (test) {
    var x = 1;
}

<pre class="language-text"><code class="language-text">code-block.js:2:5 <a href="https://biomejs.dev/linter/rules/no-inner-declarations">lint/correctness/noInnerDeclarations</a> ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ ✖ This var should be declared at the root of the module. 1 │ if (test) { > 2 │ var x = 1; │ ^^^^^^^^^ 3 │ } 4 │ ℹ The var is accessible in the whole body of the module. To avoid confusion, it should be declared at the root of the module. </code></pre>

cjs

function f() {
    if (test) {
        function g() {}
    }
}

<pre class="language-text"><code class="language-text">code-block.cjs:3:9 <a href="https://biomejs.dev/linter/rules/no-inner-declarations">lint/correctness/noInnerDeclarations</a> ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ ✖ This function should be declared at the root of the enclosing function. 1 │ function f() { 2 │ if (test) { > 3 │ function g() {} │ ^^^^^^^^^^^^^^^ 4 │ } 5 │ } ℹ The function is accessible in the whole body of the enclosing function. To avoid confusion, it should be declared at the root of the enclosing function. </code></pre>

function f() {
    if (test) {
        var x = 1;
    }
}

<pre class="language-text"><code class="language-text">code-block.js:3:9 <a href="https://biomejs.dev/linter/rules/no-inner-declarations">lint/correctness/noInnerDeclarations</a> ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ ✖ This var should be declared at the root of the enclosing function. 1 │ function f() { 2 │ if (test) { > 3 │ var x = 1; │ ^^^^^^^^^ 4 │ } 5 │ } ℹ The var is accessible in the whole body of the enclosing function. To avoid confusion, it should be declared at the root of the enclosing function. </code></pre>

Valid

// inside a module, function declarations are block-scoped and thus allowed.
if (test) {
    function f() {}
}
export {}

function f() { }

function f() {
    function g() {}
}

function f() {
    var x = 1;
}

function f() {
    if (test) {
        const g = function() {};
    }
}

</TabItem> </Tabs>

How to configure

Description

Examples

Invalid

Valid

Related links