noUselessStringConcat

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

<Tabs> <TabItem label="JavaScript (and super languages)" icon="seti:javascript"> ## Summary - Rule available since: `v1.8.0` - Diagnostic Category: [`lint/complexity/noUselessStringConcat`](/reference/diagnostics#diagnostic-category) - This rule isn't recommended, so you need to enable it. - This rule has a [**safe**](/linter/#safe-fixes) fix. - The default severity of this rule is [**information**](/reference/diagnostics#information). - Sources: - Same as [`no-useless-concat`](https://eslint.org/docs/latest/rules/no-useless-concat)

How to configure

json

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

Description

Disallow unnecessary concatenation of string or template literals.

This rule aims to flag concatenation of string or template literals when they could be combined into a single literal. Notably, this also includes concatenating a string with a number (unlike the derivative ESLint rule).

Concatenation of multiple strings is allowed for multi-line strings (such as ones used to prevent exceeding the maximum line width).

Examples

Invalid

const a = "a" + "b";

<pre class="language-text"><code class="language-text">code-block.js:1:11 <a href="https://biomejs.dev/linter/rules/no-useless-string-concat">lint/complexity/noUselessStringConcat</a> FIXABLE ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ ℹ Useless string concatenation. > 1 │ const a = "a" + "b"; │ ^^^^^^^^^ 2 │ ℹ Consider turning the expression into a single string to improve readability and runtime performance. ℹ Safe fix: Remove the useless concatenation 1 │ - const·a·=·"a"·+·"b"; 1 │ + const·a·=·"ab"; 2 2 │ </code></pre>

const foo = "string" + 123;

<pre class="language-text"><code class="language-text">code-block.js:1:13 <a href="https://biomejs.dev/linter/rules/no-useless-string-concat">lint/complexity/noUselessStringConcat</a> FIXABLE ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ ℹ Useless string concatenation. > 1 │ const foo = "string" + 123; │ ^^^^^^^^^^^^^^ 2 │ ℹ Consider turning the expression into a single string to improve readability and runtime performance. ℹ Safe fix: Remove the useless concatenation 1 │ - const·foo·=·"string"·+·123; 1 │ + const·foo·=·"string123"; 2 2 │ </code></pre>

const a = "a" + "b" + "c";

<pre class="language-text"><code class="language-text">code-block.js:1:11 <a href="https://biomejs.dev/linter/rules/no-useless-string-concat">lint/complexity/noUselessStringConcat</a> FIXABLE ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ ℹ Useless string concatenation. > 1 │ const a = "a" + "b" + "c"; │ ^^^^^^^^^^^^^^^ 2 │ ℹ Consider turning the expression into a single string to improve readability and runtime performance. ℹ Safe fix: Remove the useless concatenation 1 │ - const·a·=·"a"·+·"b"·+·"c"; 1 │ + const·a·=·"abc"; 2 2 │ </code></pre>

const a = (foo + "a") + ("b" + "c");

<pre class="language-text"><code class="language-text">code-block.js:1:26 <a href="https://biomejs.dev/linter/rules/no-useless-string-concat">lint/complexity/noUselessStringConcat</a> FIXABLE ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ ℹ Useless string concatenation. > 1 │ const a = (foo + "a") + ("b" + "c"); │ ^^^^^^^^^ 2 │ ℹ Consider turning the expression into a single string to improve readability and runtime performance. ℹ Safe fix: Remove the useless concatenation 1 │ - const·a·=·(foo·+·"a")·+·("b"·+·"c"); 1 │ + const·a·=·(foo·+·"a")·+·("bc"); 2 2 │ </code></pre>

Valid

const a = 1 + 1;

const a = 1 * '2';

const a = 1 - 2;

const a = foo + bar;

const a = 'foo' + bar;

Multi-line strings are ignored:

const multiline = 'foo' + // formatting
          'bar'

const alsoMultiline = 'foo'
          + 'bar'
          + `baz`

</TabItem> </Tabs>

How to configure

Description

Examples

Invalid

Valid

Related links