noInvalidUseBeforeDeclaration

JavaScript (and super languages)

摘要

¥Summary

规则生效日期：v1.5.0

¥Rule available since: v1.5.0
诊断类别：lint/correctness/noInvalidUseBeforeDeclaration

¥Diagnostic Category: lint/correctness/noInvalidUseBeforeDeclaration
此规则为推荐规则，默认启用。

¥This rule is recommended, which means is enabled by default.
此规则没有修复方案。

¥This rule doesn’t have a fix.
此规则的默认严重级别为 error。

¥The default severity of this rule is error.
来源：

¥Sources:
- 与 no-use-before-define 相同
  
  ¥Same as no-use-before-define
- 与 @typescript-eslint/no-use-before-define 相同
  
  ¥Same as @typescript-eslint/no-use-before-define

如何配置

¥How to configure

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{
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  "linter": {
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    "rules": {
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      "correctness": {
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        "noInvalidUseBeforeDeclaration": "error"
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      }
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    }
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  }
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}

描述

¥Description

禁止在声明之前使用变量、函数参数、类和枚举。

¥Disallow the use of variables, function parameters, classes, and enums before their declaration

JavaScript 不允许在声明之前使用块级作用域变量（let、const）、函数参数和类。同样，TypeScript 不允许在枚举声明之前使用枚举。在声明变量或参数之前，任何尝试访问该变量或参数都会抛出 ReferenceError。

¥JavaScript doesn’t allow the use of block-scoped variables (let, const), function parameters, and classes before their declaration. Similarly TypeScript doesn’t allow the use of enums before their declaration. A ReferenceError will be thrown with any attempt to access the variable or the parameter before its declaration.

该规则还报告在声明之前使用 var 声明的变量的使用情况。

¥The rule also reports the use of variables declared with var before their declarations.

示例

¥Examples

无效

¥Invalid

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function f() {
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    console.log(x);
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    let x;
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}

code-block.js:2:17 lint/correctness/noInvalidUseBeforeDeclaration ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ This variable is used before its declaration.
  
    1 │ function f() {
  > 2 │     console.log(x);
      │                 ^
    3 │     let x;
    4 │ }
  
  ℹ The variable is declared here:
  
    1 │ function f() {
    2 │     console.log(x);
  > 3 │     let x;
      │         ^
    4 │ }
    5 │

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function f() {
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    console.log(x);
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    var x = 0;
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}

code-block.js:2:17 lint/correctness/noInvalidUseBeforeDeclaration ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ This variable is used before its declaration.
  
    1 │ function f() {
  > 2 │     console.log(x);
      │                 ^
    3 │     var x = 0;
    4 │ }
  
  ℹ The variable is declared here:
  
    1 │ function f() {
    2 │     console.log(x);
  > 3 │     var x = 0;
      │         ^
    4 │ }
    5 │

1
function f(a = b, b = 0) {}

code-block.js:1:16 lint/correctness/noInvalidUseBeforeDeclaration ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ This parameter is used before its declaration.
  
  > 1 │ function f(a = b, b = 0) {}
      │                ^
    2 │ 
  
  ℹ The parameter is declared here:
  
  > 1 │ function f(a = b, b = 0) {}
      │                   ^
    2 │

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new C();
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class C {}

code-block.js:1:5 lint/correctness/noInvalidUseBeforeDeclaration ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ This class is used before its declaration.
  
  > 1 │ new C();
      │     ^
    2 │ class C {}
    3 │ 
  
  ℹ The class is declared here:
  
    1 │ new C();
  > 2 │ class C {}
      │       ^
    3 │

有效

¥Valid

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f();
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function f() {}

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// An export can reference a variable before its declaration.
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export { CONSTANT };
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const CONSTANT = 0;

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function f() { return CONSTANT; }
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const CONSTANT = 0;

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function f() {
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    new C();
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}
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let c: C;
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class C {}

noInvalidUseBeforeDeclaration

摘要

如何配置

描述

示例

无效

有效

相关链接