noBarrelFile

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JavaScript (and super languages)

Summary

Rule available since: v1.6.0
Diagnostic Category: lint/performance/noBarrelFile
This rule doesn’t have a fix.
The default severity of this rule is warning.
Sources:
- Inspired from barrel-files/avoid-barrel-files

How to configure

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{
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  "linter": {
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    "rules": {
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      "performance": {
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        "noBarrelFile": "error"
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      }
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    }
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  }
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}

Description

Disallow the use of barrel file.

A barrel file is a file that re-exports all of the exports from other files in a directory. This structure results in the unnecessary loading of many modules, significantly impacting performance in large-scale applications. Additionally, it complicates the codebase, making it difficult to navigate and understand the project’s dependency graph. This rule ignores .d.ts files and type-only exports.

For a more detailed explanation, check out https://marvinh.dev/blog/speeding-up-javascript-ecosystem-part-7/

Examples

Invalid

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export * from "foo";
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export * from "bar";

code-block.js:1:1 lint/performance/noBarrelFile ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ⚠ Avoid barrel files, they slow down performance, and cause large module graphs with modules that go unused.
  
  > 1 │ export * from “foo”;
      │ ^^^^^^^^^^^^^^^^^^^^
    2 │ export * from “bar”;
    3 │ 
  
  ℹ Check this thorough explanation to better understand the context.

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export { foo } from "foo";
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export { bar } from "bar";

code-block.js:1:1 lint/performance/noBarrelFile ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ⚠ Avoid barrel files, they slow down performance, and cause large module graphs with modules that go unused.
  
  > 1 │ export { foo } from “foo”;
      │ ^^^^^^^^^^^^^^^^^^^^^^^^^^
    2 │ export { bar } from “bar”;
    3 │ 
  
  ℹ Check this thorough explanation to better understand the context.

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export { default as module1 } from "./module1";

code-block.js:1:1 lint/performance/noBarrelFile ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ⚠ Avoid barrel files, they slow down performance, and cause large module graphs with modules that go unused.
  
  > 1 │ export { default as module1 } from “./module1”;
      │ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    2 │ 
  
  ℹ Check this thorough explanation to better understand the context.

Valid

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export type * from "foo";
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export type { foo } from "foo";