110 lines
3.5 KiB
Plaintext
110 lines
3.5 KiB
Plaintext
# import/no-duplicates
|
|
|
|
⚠️ This rule _warns_ in the following configs: ☑️ `recommended`, 🚸 `warnings`.
|
|
|
|
🔧 This rule is automatically fixable by the [`--fix` CLI option](https://eslint.org/docs/latest/user-guide/command-line-interface#--fix).
|
|
|
|
<!-- end auto-generated rule header -->
|
|
|
|
Reports if a resolved path is imported more than once.
|
|
|
|
ESLint core has a similar rule ([`no-duplicate-imports`](https://eslint.org/docs/rules/no-duplicate-imports)), but this version
|
|
is different in two key ways:
|
|
|
|
1. the paths in the source code don't have to exactly match, they just have to point to the same module on the filesystem. (i.e. `./foo` and `./foo.js`)
|
|
2. this version distinguishes Flow `type` imports from standard imports. ([#334](https://github.com/import-js/eslint-plugin-import/pull/334))
|
|
|
|
## Rule Details
|
|
|
|
Valid:
|
|
|
|
```js
|
|
import SomeDefaultClass, * as names from './mod'
|
|
// Flow `type` import from same module is fine
|
|
import type SomeType from './mod'
|
|
```
|
|
|
|
...whereas here, both `./mod` imports will be reported:
|
|
|
|
```js
|
|
import SomeDefaultClass from './mod'
|
|
|
|
// oops, some other import separated these lines
|
|
import foo from './some-other-mod'
|
|
|
|
import * as names from './mod'
|
|
|
|
// will catch this too, assuming it is the same target module
|
|
import { something } from './mod.js'
|
|
```
|
|
|
|
The motivation is that this is likely a result of two developers importing different
|
|
names from the same module at different times (and potentially largely different
|
|
locations in the file.) This rule brings both (or n-many) to attention.
|
|
|
|
### Query Strings
|
|
|
|
By default, this rule ignores query strings (i.e. paths followed by a question mark), and thus imports from `./mod?a` and `./mod?b` will be considered as duplicates. However you can use the option `considerQueryString` to handle them as different (primarily because browsers will resolve those imports differently).
|
|
|
|
Config:
|
|
|
|
```json
|
|
"import/no-duplicates": ["error", {"considerQueryString": true}]
|
|
```
|
|
|
|
And then the following code becomes valid:
|
|
|
|
```js
|
|
import minifiedMod from './mod?minify'
|
|
import noCommentsMod from './mod?comments=0'
|
|
import originalMod from './mod'
|
|
```
|
|
|
|
It will still catch duplicates when using the same module and the exact same query string:
|
|
|
|
```js
|
|
import SomeDefaultClass from './mod?minify'
|
|
|
|
// This is invalid, assuming `./mod` and `./mod.js` are the same target:
|
|
import * from './mod.js?minify'
|
|
```
|
|
|
|
### Inline Type imports
|
|
|
|
TypeScript 4.5 introduced a new [feature](https://devblogs.microsoft.com/typescript/announcing-typescript-4-5/#type-on-import-names) that allows mixing of named value and type imports. In order to support fixing to an inline type import when duplicate imports are detected, `prefer-inline` can be set to true.
|
|
|
|
Config:
|
|
|
|
```json
|
|
"import/no-duplicates": ["error", {"prefer-inline": true}]
|
|
```
|
|
|
|
<!--tabs-->
|
|
|
|
❌ Invalid `["error", {"prefer-inline": true}]`
|
|
|
|
```js
|
|
import { AValue, type AType } from './mama-mia'
|
|
import type { BType } from './mama-mia'
|
|
|
|
import { CValue } from './papa-mia'
|
|
import type { CType } from './papa-mia'
|
|
```
|
|
|
|
✅ Valid with `["error", {"prefer-inline": true}]`
|
|
|
|
```js
|
|
import { AValue, type AType, type BType } from './mama-mia'
|
|
|
|
import { CValue, type CType } from './papa-mia'
|
|
```
|
|
|
|
<!--tabs-->
|
|
|
|
## When Not To Use It
|
|
|
|
If the core ESLint version is good enough (i.e. you're _not_ using Flow and you _are_ using [`import/extensions`](./extensions.md)), keep it and don't use this.
|
|
|
|
If you like to split up imports across lines or may need to import a default and a namespace,
|
|
you may not want to enable this rule.
|