noPathConcat (JavaScript)

Language JavaScript (and super languages)

Summary

Rule available since: v2.6.3
Diagnostic Category: lint/nursery/noPathConcat
This rule doesn’t have a fix.
The default severity of this rule is warning.
Sources:
- Same as n/no-path-concat

How to configure

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{
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  "linter": {
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    "rules": {
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      "nursery": {
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        "noPathConcat": "error"
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      }
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    }
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  }
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}

Description

Disallow building file paths and URLs by joining strings to __dirname, __filename, or import.meta values.

In Node.js, __dirname and __filename hold the folder and the path of the current file. import.meta.dirname and import.meta.filename hold the same values in ES modules. Adding a string to one of them is a common way to point at another file, but the character that separates folders depends on the operating system: Windows uses \, while Linux and macOS use /. Joining strings can also leave two separators in a row.

Use path.join() or path.resolve() from the node:path module instead. They insert the right separator for the system the code runs on.

import.meta.url is a URL such as file:///project/src/index.js, not a file path. Adding /foo.js to it gives file:///project/src/index.js/foo.js, which doesn’t point to a file next to the current one. Use new URL() to build a URL that is relative to import.meta.url.

The rule reports one of these values only when the text added right after it starts with /, \, or the sep value of the node:path module. Adding other text, such as a file extension, is allowed. The rule doesn’t look up the value of a variable that is added, so __dirname + suffix is never reported.

Examples

Invalid

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const fullPath = __dirname + "/foo.js";

code-block.js:1:18 lint/nursery/noPathConcat ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ⚠ This file path is built by joining strings.
  
  > 1 │ const fullPath = __dirname + "/foo.js";
      │                  ^^^^^^^^^^^^^^^^^^^^^
    2 │ 
  
  ℹ The character that separates folders depends on the operating system, and joining strings can leave two separators in a row.
  
  ℹ Use path.join() or path.resolve() from the node:path module instead.
  
  ℹ This rule belongs to the nursery group, which means it is not yet stable and may change in the future. Visit https://biomejs.dev/linter/#nursery for more information.

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const fullPath = `${__filename}/foo.js`;

code-block.js:1:18 lint/nursery/noPathConcat ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ⚠ This file path is built by joining strings.
  
  > 1 │ const fullPath = `${__filename}/foo.js`;
      │                  ^^^^^^^^^^^^^^^^^^^^^^
    2 │ 
  
  ℹ The character that separates folders depends on the operating system, and joining strings can leave two separators in a row.
  
  ℹ Use path.join() or path.resolve() from the node:path module instead.
  
  ℹ This rule belongs to the nursery group, which means it is not yet stable and may change in the future. Visit https://biomejs.dev/linter/#nursery for more information.

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const fullPath = import.meta.dirname + "/foo.js";

code-block.js:1:18 lint/nursery/noPathConcat ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ⚠ This file path is built by joining strings.
  
  > 1 │ const fullPath = import.meta.dirname + "/foo.js";
      │                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    2 │ 
  
  ℹ The character that separates folders depends on the operating system, and joining strings can leave two separators in a row.
  
  ℹ Use path.join() or path.resolve() from the node:path module instead.
  
  ℹ This rule belongs to the nursery group, which means it is not yet stable and may change in the future. Visit https://biomejs.dev/linter/#nursery for more information.

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import path from "node:path";
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const fullPath = __dirname + path.sep + "foo.js";

code-block.js:2:18 lint/nursery/noPathConcat ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ⚠ This file path is built by joining strings.
  
    1 │ import path from "node:path";
  > 2 │ const fullPath = __dirname + path.sep + "foo.js";
      │                  ^^^^^^^^^^^^^^^^^^^^
    3 │ 
  
  ℹ The character that separates folders depends on the operating system, and joining strings can leave two separators in a row.
  
  ℹ Use path.join() or path.resolve() from the node:path module instead.
  
  ℹ This rule belongs to the nursery group, which means it is not yet stable and may change in the future. Visit https://biomejs.dev/linter/#nursery for more information.

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const fullUrl = import.meta.url + "/foo.js";

code-block.js:1:17 lint/nursery/noPathConcat ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ⚠ This URL is built by joining strings.
  
  > 1 │ const fullUrl = import.meta.url + "/foo.js";
      │                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
    2 │ 
  
  ℹ import.meta.url is the URL of the current file, so text added to its end doesn't point to a file next to it.
  
  ℹ Use new URL() instead, for example new URL("./foo.js", import.meta.url).
  
  ℹ This rule belongs to the nursery group, which means it is not yet stable and may change in the future. Visit https://biomejs.dev/linter/#nursery for more information.

Valid

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import path from "node:path";
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const fullPath1 = path.join(__dirname, "foo.js");
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const fullPath2 = path.resolve(import.meta.dirname, "foo.js");
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const fullPath3 = __filename + ".map";
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const fullPath4 = `${__dirname}_backup`;
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const fullUrl = new URL("./foo.js", import.meta.url);