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src/content/docs/linter/rules/use-template.mdx

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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/useTemplate`](/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 [`prefer-template`](https://eslint.org/docs/latest/rules/prefer-template)

How to configure

json
{
	"linter": {
		"rules": {
			"style": {
				"useTemplate": "error"
			}
		}
	}
}

Description

Prefer template literals over string concatenation.

Examples

Invalid

js
const s = foo + "baz";
<pre class="language-text"><code class="language-text">code-block.js:1:11 <a href="https://biomejs.dev/linter/rules/use-template">lint/style/useTemplate</a> <span style="color: #000; background-color: #ddd;"> FIXABLE </span> ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;"><strong>Template</strong></span><span style="color: lightgreen;"> literals are preferred over </span><span style="color: lightgreen;"><strong>string concatenation.</strong></span> <strong><span style="color: Tomato;">&gt;</span></strong> <strong>1 │ </strong>const s = foo + &quot;baz&quot;; <strong> │ </strong> <strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong> <strong>2 │ </strong> <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">Unsafe fix</span><span style="color: lightgreen;">: </span><span style="color: lightgreen;">Use a </span><span style="color: lightgreen;"><strong>template literal</strong></span><span style="color: lightgreen;">.</span> <strong>1</strong> <strong> │ </strong><span style="color: Tomato;">-</span> <span style="color: Tomato;">c</span><span style="color: Tomato;">o</span><span style="color: Tomato;">n</span><span style="color: Tomato;">s</span><span style="color: Tomato;">t</span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;">s</span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;">=</span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;">f</span><span style="color: Tomato;">o</span><span style="color: Tomato;">o</span><span style="color: Tomato;"><span style="opacity: 0.8;"><strong>·</strong></span></span><span style="color: Tomato;"><strong>+</strong></span><span style="color: Tomato;"><span style="opacity: 0.8;"><strong>·</strong></span></span><span style="color: Tomato;"><strong>&quot;</strong></span><span style="color: Tomato;">b</span><span style="color: Tomato;">a</span><span style="color: Tomato;">z</span><span style="color: Tomato;"><strong>&quot;</strong></span><span style="color: Tomato;">;</span> <strong>1</strong><strong> │ </strong><span style="color: MediumSeaGreen;">+</span> <span style="color: MediumSeaGreen;">c</span><span style="color: MediumSeaGreen;">o</span><span style="color: MediumSeaGreen;">n</span><span style="color: MediumSeaGreen;">s</span><span style="color: MediumSeaGreen;">t</span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;">s</span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;">=</span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;"><strong>&#96;</strong></span><span style="color: MediumSeaGreen;"><strong>$</strong></span><span style="color: MediumSeaGreen;"><strong>&#123;</strong></span><span style="color: MediumSeaGreen;">f</span><span style="color: MediumSeaGreen;">o</span><span style="color: MediumSeaGreen;">o</span><span style="color: MediumSeaGreen;"><strong>&#125;</strong></span><span style="color: MediumSeaGreen;">b</span><span style="color: MediumSeaGreen;">a</span><span style="color: MediumSeaGreen;">z</span><span style="color: MediumSeaGreen;"><strong>&#96;</strong></span><span style="color: MediumSeaGreen;">;</span> <strong>2</strong> <strong>2</strong><strong> │ </strong> </code></pre>
js
const s = 1 + 2 + "foo" + 3;
<pre class="language-text"><code class="language-text">code-block.js:1:11 <a href="https://biomejs.dev/linter/rules/use-template">lint/style/useTemplate</a> <span style="color: #000; background-color: #ddd;"> FIXABLE </span> ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;"><strong>Template</strong></span><span style="color: lightgreen;"> literals are preferred over </span><span style="color: lightgreen;"><strong>string concatenation.</strong></span> <strong><span style="color: Tomato;">&gt;</span></strong> <strong>1 │ </strong>const s = 1 + 2 + &quot;foo&quot; + 3; <strong> │ </strong> <strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong> <strong>2 │ </strong> <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">Unsafe fix</span><span style="color: lightgreen;">: </span><span style="color: lightgreen;">Use a </span><span style="color: lightgreen;"><strong>template literal</strong></span><span style="color: lightgreen;">.</span> <strong>1</strong> <strong> │ </strong><span style="color: Tomato;">-</span> <span style="color: Tomato;">c</span><span style="color: Tomato;">o</span><span style="color: Tomato;">n</span><span style="color: Tomato;">s</span><span style="color: Tomato;">t</span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;">s</span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;">=</span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;">1</span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;">+</span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;">2</span><span style="color: Tomato;"><span style="opacity: 0.8;"><strong>·</strong></span></span><span style="color: Tomato;"><strong>+</strong></span><span style="color: Tomato;"><span style="opacity: 0.8;"><strong>·</strong></span></span><span style="color: Tomato;"><strong>&quot;</strong></span><span style="color: Tomato;">f</span><span style="color: Tomato;">o</span><span style="color: Tomato;">o</span><span style="color: Tomato;"><strong>&quot;</strong></span><span style="color: Tomato;"><span style="opacity: 0.8;"><strong>·</strong></span></span><span style="color: Tomato;"><strong>+</strong></span><span style="color: Tomato;"><span style="opacity: 0.8;"><strong>·</strong></span></span><span style="color: Tomato;">3</span><span style="color: Tomato;">;</span> <strong>1</strong><strong> │ </strong><span style="color: MediumSeaGreen;">+</span> <span style="color: MediumSeaGreen;">c</span><span style="color: MediumSeaGreen;">o</span><span style="color: MediumSeaGreen;">n</span><span style="color: MediumSeaGreen;">s</span><span style="color: MediumSeaGreen;">t</span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;">s</span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;">=</span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;"><strong>&#96;</strong></span><span style="color: MediumSeaGreen;"><strong>$</strong></span><span style="color: MediumSeaGreen;"><strong>&#123;</strong></span><span style="color: MediumSeaGreen;">1</span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;">+</span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;">2</span><span style="color: MediumSeaGreen;"><strong>&#125;</strong></span><span style="color: MediumSeaGreen;">f</span><span style="color: MediumSeaGreen;">o</span><span style="color: MediumSeaGreen;">o</span><span style="color: MediumSeaGreen;"><strong>$</strong></span><span style="color: MediumSeaGreen;"><strong>&#123;</strong></span><span style="color: MediumSeaGreen;">3</span><span style="color: MediumSeaGreen;"><strong>&#125;</strong></span><span style="color: MediumSeaGreen;"><strong>&#96;</strong></span><span style="color: MediumSeaGreen;">;</span> <strong>2</strong> <strong>2</strong><strong> │ </strong> </code></pre>
js
const s = 1 * 2 + "foo";
<pre class="language-text"><code class="language-text">code-block.js:1:11 <a href="https://biomejs.dev/linter/rules/use-template">lint/style/useTemplate</a> <span style="color: #000; background-color: #ddd;"> FIXABLE </span> ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;"><strong>Template</strong></span><span style="color: lightgreen;"> literals are preferred over </span><span style="color: lightgreen;"><strong>string concatenation.</strong></span> <strong><span style="color: Tomato;">&gt;</span></strong> <strong>1 │ </strong>const s = 1 &#42; 2 + &quot;foo&quot;; <strong> │ </strong> <strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong> <strong>2 │ </strong> <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">Unsafe fix</span><span style="color: lightgreen;">: </span><span style="color: lightgreen;">Use a </span><span style="color: lightgreen;"><strong>template literal</strong></span><span style="color: lightgreen;">.</span> <strong>1</strong> <strong> │ </strong><span style="color: Tomato;">-</span> <span style="color: Tomato;">c</span><span style="color: Tomato;">o</span><span style="color: Tomato;">n</span><span style="color: Tomato;">s</span><span style="color: Tomato;">t</span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;">s</span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;">=</span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;">1</span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;">&#42;</span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;">2</span><span style="color: Tomato;"><span style="opacity: 0.8;"><strong>·</strong></span></span><span style="color: Tomato;"><strong>+</strong></span><span style="color: Tomato;"><span style="opacity: 0.8;"><strong>·</strong></span></span><span style="color: Tomato;"><strong>&quot;</strong></span><span style="color: Tomato;">f</span><span style="color: Tomato;">o</span><span style="color: Tomato;">o</span><span style="color: Tomato;"><strong>&quot;</strong></span><span style="color: Tomato;">;</span> <strong>1</strong><strong> │ </strong><span style="color: MediumSeaGreen;">+</span> <span style="color: MediumSeaGreen;">c</span><span style="color: MediumSeaGreen;">o</span><span style="color: MediumSeaGreen;">n</span><span style="color: MediumSeaGreen;">s</span><span style="color: MediumSeaGreen;">t</span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;">s</span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;">=</span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;"><strong>&#96;</strong></span><span style="color: MediumSeaGreen;"><strong>$</strong></span><span style="color: MediumSeaGreen;"><strong>&#123;</strong></span><span style="color: MediumSeaGreen;">1</span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;">&#42;</span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;">2</span><span style="color: MediumSeaGreen;"><strong>&#125;</strong></span><span style="color: MediumSeaGreen;">f</span><span style="color: MediumSeaGreen;">o</span><span style="color: MediumSeaGreen;">o</span><span style="color: MediumSeaGreen;"><strong>&#96;</strong></span><span style="color: MediumSeaGreen;">;</span> <strong>2</strong> <strong>2</strong><strong> │ </strong> </code></pre>
js
const s = 1 + "foo" + 2 + "bar" + "baz" + 3;
<pre class="language-text"><code class="language-text">code-block.js:1:11 <a href="https://biomejs.dev/linter/rules/use-template">lint/style/useTemplate</a> <span style="color: #000; background-color: #ddd;"> FIXABLE </span> ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;"><strong>Template</strong></span><span style="color: lightgreen;"> literals are preferred over </span><span style="color: lightgreen;"><strong>string concatenation.</strong></span> <strong><span style="color: Tomato;">&gt;</span></strong> <strong>1 │ </strong>const s = 1 + &quot;foo&quot; + 2 + &quot;bar&quot; + &quot;baz&quot; + 3; <strong> │ </strong> <strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong> <strong>2 │ </strong> <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">Unsafe fix</span><span style="color: lightgreen;">: </span><span style="color: lightgreen;">Use a </span><span style="color: lightgreen;"><strong>template literal</strong></span><span style="color: lightgreen;">.</span> <strong>1</strong> <strong> │ </strong><span style="color: Tomato;">-</span> <span style="color: Tomato;">c</span><span style="color: Tomato;">o</span><span style="color: Tomato;">n</span><span style="color: Tomato;">s</span><span style="color: Tomato;">t</span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;">s</span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;">=</span><span style="color: Tomato;"><span style="opacity: 0.8;">·</span></span><span style="color: Tomato;">1</span><span style="color: Tomato;"><span style="opacity: 0.8;"><strong>·</strong></span></span><span style="color: Tomato;"><strong>+</strong></span><span style="color: Tomato;"><span style="opacity: 0.8;"><strong>·</strong></span></span><span style="color: Tomato;"><strong>&quot;</strong></span><span style="color: Tomato;">f</span><span style="color: Tomato;">o</span><span style="color: Tomato;">o</span><span style="color: Tomato;"><strong>&quot;</strong></span><span style="color: Tomato;"><span style="opacity: 0.8;"><strong>·</strong></span></span><span style="color: Tomato;"><strong>+</strong></span><span style="color: Tomato;"><span style="opacity: 0.8;"><strong>·</strong></span></span><span style="color: Tomato;">2</span><span style="color: Tomato;"><span style="opacity: 0.8;"><strong>·</strong></span></span><span style="color: Tomato;"><strong>+</strong></span><span style="color: Tomato;"><span style="opacity: 0.8;"><strong>·</strong></span></span><span style="color: Tomato;"><strong>&quot;</strong></span><span style="color: Tomato;"><strong>b</strong></span><span style="color: Tomato;"><strong>a</strong></span><span style="color: Tomato;"><strong>r</strong></span><span style="color: Tomato;"><strong>&quot;</strong></span><span style="color: Tomato;"><span style="opacity: 0.8;"><strong>·</strong></span></span><span style="color: Tomato;"><strong>+</strong></span><span style="color: Tomato;"><span style="opacity: 0.8;"><strong>·</strong></span></span><span style="color: Tomato;"><strong>&quot;</strong></span><span style="color: Tomato;"><strong>b</strong></span><span style="color: Tomato;"><strong>a</strong></span><span style="color: Tomato;"><strong>z</strong></span><span style="color: Tomato;"><strong>&quot;</strong></span><span style="color: Tomato;"><span style="opacity: 0.8;"><strong>·</strong></span></span><span style="color: Tomato;"><strong>+</strong></span><span style="color: Tomato;"><span style="opacity: 0.8;"><strong>·</strong></span></span><span style="color: Tomato;">3</span><span style="color: Tomato;">;</span> <strong>1</strong><strong> │ </strong><span style="color: MediumSeaGreen;">+</span> <span style="color: MediumSeaGreen;">c</span><span style="color: MediumSeaGreen;">o</span><span style="color: MediumSeaGreen;">n</span><span style="color: MediumSeaGreen;">s</span><span style="color: MediumSeaGreen;">t</span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;">s</span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;">=</span><span style="color: MediumSeaGreen;"><span style="opacity: 0.8;">·</span></span><span style="color: MediumSeaGreen;"><strong>&#96;</strong></span><span style="color: MediumSeaGreen;"><strong>$</strong></span><span style="color: MediumSeaGreen;"><strong>&#123;</strong></span><span style="color: MediumSeaGreen;">1</span><span style="color: MediumSeaGreen;"><strong>&#125;</strong></span><span style="color: MediumSeaGreen;">f</span><span style="color: MediumSeaGreen;">o</span><span style="color: MediumSeaGreen;">o</span><span style="color: MediumSeaGreen;"><strong>$</strong></span><span style="color: MediumSeaGreen;"><strong>&#123;</strong></span><span style="color: MediumSeaGreen;">2</span><span style="color: MediumSeaGreen;"><strong>&#125;</strong></span><span style="color: MediumSeaGreen;"><strong>b</strong></span><span style="color: MediumSeaGreen;"><strong>a</strong></span><span style="color: MediumSeaGreen;"><strong>r</strong></span><span style="color: MediumSeaGreen;"><strong>b</strong></span><span style="color: MediumSeaGreen;"><strong>a</strong></span><span style="color: MediumSeaGreen;"><strong>z</strong></span><span style="color: MediumSeaGreen;"><strong>$</strong></span><span style="color: MediumSeaGreen;"><strong>&#123;</strong></span><span style="color: MediumSeaGreen;">3</span><span style="color: MediumSeaGreen;"><strong>&#125;</strong></span><span style="color: MediumSeaGreen;"><strong>&#96;</strong></span><span style="color: MediumSeaGreen;">;</span> <strong>2</strong> <strong>2</strong><strong> │ </strong> </code></pre>

Valid

js
let s = "foo" + "bar" + `baz`;
js
let s = `value: ${1}`;
</TabItem> </Tabs>