no-unused-expressions

Disallow unused expressions.

✅

在 ESLint 配置 中扩展"plugin:@typescript-eslint/recommended" 可启用此规则。

🧱

This is an "extension" rule that replaces a core ESLint rule to work with TypeScript. See Rules > Extension Rules.

This rule extends the base no-unused-expressions rule from ESLint core. 它支持 TypeScript 特定的表达式：

¥It supports TypeScript-specific expressions:

• 将模块声明（"use strict" 等）中的指令标记为未使用

  ¥Marks directives in modules declarations ("use strict", etc.) as not unused

• 如果以下表达式的封装值表达式未使用，则将其标记为未使用：

  ¥Marks the following expressions as unused if their wrapped value expressions are unused:

  • 断言表达式：x as number;, x!;, <number>x;

    ¥Assertion expressions: x as number;, x!;, <number>x;

  • 实例化表达式：Set<number>;

    ¥Instantiation expressions: Set<number>;

尽管类型表达式永远不会产生运行时副作用（即 x!; 与 x; 相同），但它们可用于断言类型以进行测试。

¥Although the type expressions never have runtime side effects (that is, x!; is the same as x;), they can be used to assert types for testing purposes.

示例

¥Examples

❌ Incorrect

Set<number>;
1 as number;
window!;

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✅ Correct

function getSet() {
  return Set;
}

// Funtion calls are allowed, so type expressions that wrap function calls are allowed
getSet()<number>;
getSet() as Set<unknown>;
getSet()!;

// Namespaces can have directives
namespace A {
  'use strict';
}

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选项

See eslint/no-unused-expressions's options.

如何使用

Flat Config

eslint.config.mjs

export default tseslint.config({
  rules: {
    // Note: you must disable the base rule as it can report incorrect errors
    "no-unused-expressions": "off",
    "@typescript-eslint/no-unused-expressions": "error"
  }
});

Legacy Config

.eslintrc.cjs

module.exports = {
  "rules": {
    // Note: you must disable the base rule as it can report incorrect errors
    "no-unused-expressions": "off",
    "@typescript-eslint/no-unused-expressions": "error"
  }
};

在线运行试试这个规则 ↗

'## 资源'

• 规则源码
• 测试源码

^{Taken with ❤️ from ESLint core.}