112 lines
3.2 KiB
Markdown
112 lines
3.2 KiB
Markdown
|
# import/no-cycle
|
||
|
|
|
||
|
|
<!-- end auto-generated rule header -->
|
||
|
|
|
||
|
|
Ensures that there is no resolvable path back to this module via its dependencies.
|
||
|
|
|
||
|
|
This includes cycles of depth 1 (imported module imports me) to `"∞"` (or `Infinity`), if the
|
||
|
|
[`maxDepth`](#maxdepth) option is not set.
|
||
|
|
|
||
|
|
```js
|
||
|
|
// dep-b.js
|
||
|
|
import './dep-a.js'
|
||
|
|
|
||
|
|
export function b() { /* ... */ }
|
||
|
|
```
|
||
|
|
|
||
|
|
```js
|
||
|
|
// dep-a.js
|
||
|
|
import { b } from './dep-b.js' // reported: Dependency cycle detected.
|
||
|
|
```
|
||
|
|
|
||
|
|
This rule does _not_ detect imports that resolve directly to the linted module;
|
||
|
|
for that, see [`no-self-import`].
|
||
|
|
|
||
|
|
This rule ignores type-only imports in Flow and TypeScript syntax (`import type` and `import typeof`), which have no runtime effect.
|
||
|
|
|
||
|
|
## Rule Details
|
||
|
|
|
||
|
|
### Options
|
||
|
|
|
||
|
|
By default, this rule only detects cycles for ES6 imports, but see the [`no-unresolved` options](./no-unresolved.md#options) as this rule also supports the same `commonjs` and `amd` flags. However, these flags only impact which import types are _linted_; the
|
||
|
|
import/export infrastructure only registers `import` statements in dependencies, so
|
||
|
|
cycles created by `require` within imported modules may not be detected.
|
||
|
|
|
||
|
|
#### `maxDepth`
|
||
|
|
|
||
|
|
There is a `maxDepth` option available to prevent full expansion of very deep dependency trees:
|
||
|
|
|
||
|
|
```js
|
||
|
|
/*eslint import/no-cycle: [2, { maxDepth: 1 }]*/
|
||
|
|
|
||
|
|
// dep-c.js
|
||
|
|
import './dep-a.js'
|
||
|
|
```
|
||
|
|
|
||
|
|
```js
|
||
|
|
// dep-b.js
|
||
|
|
import './dep-c.js'
|
||
|
|
|
||
|
|
export function b() { /* ... */ }
|
||
|
|
```
|
||
|
|
|
||
|
|
```js
|
||
|
|
// dep-a.js
|
||
|
|
import { b } from './dep-b.js' // not reported as the cycle is at depth 2
|
||
|
|
```
|
||
|
|
|
||
|
|
This is not necessarily recommended, but available as a cost/benefit tradeoff mechanism
|
||
|
|
for reducing total project lint time, if needed.
|
||
|
|
|
||
|
|
#### `ignoreExternal`
|
||
|
|
|
||
|
|
An `ignoreExternal` option is available to prevent the cycle detection to expand to external modules:
|
||
|
|
|
||
|
|
```js
|
||
|
|
/*eslint import/no-cycle: [2, { ignoreExternal: true }]*/
|
||
|
|
|
||
|
|
// dep-a.js
|
||
|
|
import 'module-b/dep-b.js'
|
||
|
|
|
||
|
|
export function a() { /* ... */ }
|
||
|
|
```
|
||
|
|
|
||
|
|
```js
|
||
|
|
// node_modules/module-b/dep-b.js
|
||
|
|
import { a } from './dep-a.js' // not reported as this module is external
|
||
|
|
```
|
||
|
|
|
||
|
|
Its value is `false` by default, but can be set to `true` for reducing total project lint time, if needed.
|
||
|
|
|
||
|
|
#### `allowUnsafeDynamicCyclicDependency`
|
||
|
|
|
||
|
|
This option disable reporting of errors if a cycle is detected with at least one dynamic import.
|
||
|
|
|
||
|
|
```js
|
||
|
|
// bar.js
|
||
|
|
import { foo } from './foo';
|
||
|
|
export const bar = foo;
|
||
|
|
|
||
|
|
// foo.js
|
||
|
|
export const foo = 'Foo';
|
||
|
|
export function getBar() { return import('./bar'); }
|
||
|
|
```
|
||
|
|
|
||
|
|
> Cyclic dependency are **always** a dangerous anti-pattern as discussed extensively in [#2265](https://github.com/import-js/eslint-plugin-import/issues/2265). Please be extra careful about using this option.
|
||
|
|
|
||
|
|
## When Not To Use It
|
||
|
|
|
||
|
|
This rule is comparatively computationally expensive. If you are pressed for lint
|
||
|
|
time, or don't think you have an issue with dependency cycles, you may not want
|
||
|
|
this rule enabled.
|
||
|
|
|
||
|
|
## Further Reading
|
||
|
|
|
||
|
|
- [Original inspiring issue](https://github.com/import-js/eslint-plugin-import/issues/941)
|
||
|
|
- Rule to detect that module imports itself: [`no-self-import`]
|
||
|
|
- [`import/external-module-folders`] setting
|
||
|
|
|
||
|
|
[`no-self-import`]: ./no-self-import.md
|
||
|
|
|
||
|
|
[`import/external-module-folders`]: ../../README.md#importexternal-module-folders
|