94 lines
2.1 KiB
Plaintext
94 lines
2.1 KiB
Plaintext
---
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description: 'Disallow the use of variables before they are defined.'
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---
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import Tabs from '@theme/Tabs';
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import TabItem from '@theme/TabItem';
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> 🛑 This file is source code, not the primary documentation location! 🛑
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>
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> See **https://typescript-eslint.io/rules/no-use-before-define** for documentation.
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This rule extends the base [`eslint/no-use-before-define`](https://eslint.org/docs/rules/no-use-before-define) rule.
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It adds support for `type`, `interface` and `enum` declarations.
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## Options
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This rule adds the following options:
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```ts
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interface Options extends BaseNoUseBeforeDefineOptions {
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enums?: boolean;
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typedefs?: boolean;
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ignoreTypeReferences?: boolean;
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}
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const defaultOptions: Options = {
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...baseNoUseBeforeDefineDefaultOptions,
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enums: true,
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typedefs: true,
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ignoreTypeReferences: true,
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};
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```
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### `enums`
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If this is `true`, this rule warns every reference to a enum before the enum declaration.
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If this is `false`, this rule will ignore references to enums, when the reference is in a child scope.
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Examples of code for the `{ "enums": true }` option:
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<Tabs>
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<TabItem value="❌ Incorrect">
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```ts option='{ "enums": true }'
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const x = Foo.FOO;
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enum Foo {
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FOO,
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}
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```
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</TabItem>
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<TabItem value="✅ Correct">
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```ts option='{ "enums": false }'
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function foo() {
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return Foo.FOO;
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}
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enum Foo {
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FOO,
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}
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```
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</TabItem>
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</Tabs>
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### `typedefs`
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If this is `true`, this rule warns every reference to a type before the type declaration.
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If this is `false`, this rule will ignore references to types.
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Examples of **correct** code for the `{ "typedefs": false }` option:
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```ts option='{ "typedefs": false }' showPlaygroundButton
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let myVar: StringOrNumber;
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type StringOrNumber = string | number;
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```
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### `ignoreTypeReferences`
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If this is `true`, this rule ignores all type references, such as in type annotations and assertions.
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If this is `false`, this will will check all type references.
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Examples of **correct** code for the `{ "ignoreTypeReferences": true }` option:
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```ts option='{ "ignoreTypeReferences": true }' showPlaygroundButton
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let var1: StringOrNumber;
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type StringOrNumber = string | number;
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let var2: Enum;
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enum Enum {}
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```
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