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noSubstr

src/content/docs/linter/rules/no-substr.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: `v1.8.2` - Diagnostic Category: [`lint/style/noSubstr`](/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 [**information**](/reference/diagnostics#information). - Sources: - Same as [`unicorn/prefer-string-slice`](https://github.com/sindresorhus/eslint-plugin-unicorn/blob/main/docs/rules/prefer-string-slice.md)

How to configure

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

Description

Enforce the use of String.slice() over String.substr() and String.substring().

String.slice() is preferred over String.substr() and String.substring() because it is a more popular option with clearer behavior, and it has a consistent counterpart in arrays.

Note that String.substr, String.substring and String.slice are not identical when arguments are passed. For detailed differences, refer to the MDN documentation:

Examples

Invalid

js
foo.substr();
<pre class="language-text"><code class="language-text">code-block.js:1:5 <a href="https://biomejs.dev/linter/rules/no-substr">lint/style/noSubstr</a> <span style="color: #000; background-color: #ddd;"> FIXABLE </span> ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">Avoid using substr and consider using slice instead.</span> <strong><span style="color: Tomato;">&gt;</span></strong> <strong>1 │ </strong>foo.substr(); <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>2 │ </strong> <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;"><strong>slice</strong></span><span style="color: lightgreen;"> is more commonly used and has a less surprising behavior.</span> <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">See </span><span style="color: lightgreen;"><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/substring#the_difference_between_substring_and_substr">MDN web docs</a></span><span style="color: lightgreen;"> for more details.</span> <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 </span><span style="color: lightgreen;"><strong>.slice()</strong></span><span style="color: lightgreen;"> instead.</span> <strong>1</strong> <strong> │ </strong><span style="color: Tomato;">-</span> <span style="color: Tomato;">f</span><span style="color: Tomato;">o</span><span style="color: Tomato;">o</span><span style="color: Tomato;">.</span><span style="color: Tomato;"><strong>s</strong></span><span style="color: Tomato;"><strong>u</strong></span><span style="color: Tomato;"><strong>b</strong></span><span style="color: Tomato;"><strong>s</strong></span><span style="color: Tomato;"><strong>t</strong></span><span style="color: Tomato;"><strong>r</strong></span><span style="color: Tomato;">(</span><span style="color: Tomato;">)</span><span style="color: Tomato;">;</span> <strong>1</strong><strong> │ </strong><span style="color: MediumSeaGreen;">+</span> <span style="color: MediumSeaGreen;">f</span><span style="color: MediumSeaGreen;">o</span><span style="color: MediumSeaGreen;">o</span><span style="color: MediumSeaGreen;">.</span><span style="color: MediumSeaGreen;"><strong>s</strong></span><span style="color: MediumSeaGreen;"><strong>l</strong></span><span style="color: MediumSeaGreen;"><strong>i</strong></span><span style="color: MediumSeaGreen;"><strong>c</strong></span><span style="color: MediumSeaGreen;"><strong>e</strong></span><span style="color: MediumSeaGreen;">(</span><span style="color: MediumSeaGreen;">)</span><span style="color: MediumSeaGreen;">;</span> <strong>2</strong> <strong>2</strong><strong> │ </strong> </code></pre>
js
foo.substring();
<pre class="language-text"><code class="language-text">code-block.js:1:5 <a href="https://biomejs.dev/linter/rules/no-substr">lint/style/noSubstr</a> <span style="color: #000; background-color: #ddd;"> FIXABLE </span> ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">Avoid using substring and consider using slice instead.</span> <strong><span style="color: Tomato;">&gt;</span></strong> <strong>1 │ </strong>foo.substring(); <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>2 │ </strong> <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;"><strong>slice</strong></span><span style="color: lightgreen;"> is more commonly used and has a less surprising behavior.</span> <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">See </span><span style="color: lightgreen;"><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/substring#the_difference_between_substring_and_substr">MDN web docs</a></span><span style="color: lightgreen;"> for more details.</span> <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 </span><span style="color: lightgreen;"><strong>.slice()</strong></span><span style="color: lightgreen;"> instead.</span> <strong>1</strong> <strong> │ </strong><span style="color: Tomato;">-</span> <span style="color: Tomato;">f</span><span style="color: Tomato;">o</span><span style="color: Tomato;">o</span><span style="color: Tomato;">.</span><span style="color: Tomato;"><strong>s</strong></span><span style="color: Tomato;"><strong>u</strong></span><span style="color: Tomato;"><strong>b</strong></span><span style="color: Tomato;"><strong>s</strong></span><span style="color: Tomato;"><strong>t</strong></span><span style="color: Tomato;"><strong>r</strong></span><span style="color: Tomato;"><strong>i</strong></span><span style="color: Tomato;"><strong>n</strong></span><span style="color: Tomato;"><strong>g</strong></span><span style="color: Tomato;">(</span><span style="color: Tomato;">)</span><span style="color: Tomato;">;</span> <strong>1</strong><strong> │ </strong><span style="color: MediumSeaGreen;">+</span> <span style="color: MediumSeaGreen;">f</span><span style="color: MediumSeaGreen;">o</span><span style="color: MediumSeaGreen;">o</span><span style="color: MediumSeaGreen;">.</span><span style="color: MediumSeaGreen;"><strong>s</strong></span><span style="color: MediumSeaGreen;"><strong>l</strong></span><span style="color: MediumSeaGreen;"><strong>i</strong></span><span style="color: MediumSeaGreen;"><strong>c</strong></span><span style="color: MediumSeaGreen;"><strong>e</strong></span><span style="color: MediumSeaGreen;">(</span><span style="color: MediumSeaGreen;">)</span><span style="color: MediumSeaGreen;">;</span> <strong>2</strong> <strong>2</strong><strong> │ </strong> </code></pre>

Valid

js
foo.slice(beginIndex, endIndex);
</TabItem> </Tabs>