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no-unsafe-type-assertion

Disallow type assertions that narrow a type.

💭

该规则需要 类型信息 才能运行，但这会带来性能方面的权衡。

类型断言是一种告诉 TypeScript 值的类型的方法。如果你使用类型断言来缩小类型，这可能很有用，但也不安全。

¥Type assertions are a way to tell TypeScript what the type of a value is. This can be useful but also unsafe if you use type assertions to narrow down a type.

此规则禁止使用类型断言来缩小类型，因为这会绕过 TypeScript 的类型检查。扩大类型的类型断言是安全的，因为 TypeScript 本质上对类型的了解较少。

¥This rule forbids using type assertions to narrow a type, as this bypasses TypeScript's type-checking. Type assertions that broaden a type are safe because TypeScript essentially knows less about a type.

与其使用类型断言来缩小类型范围，不如依赖类型保护，这有助于避免由不安全的类型断言导致的潜在运行时错误。

¥Instead of using type assertions to narrow a type, it's better to rely on type guards, which help avoid potential runtime errors caused by unsafe type assertions.

eslint.config.mjs
export default tseslint.config({
  rules: {
    "@typescript-eslint/no-unsafe-type-assertion": "error"
  }
});

在线运行试试这个规则 ↗

示例​

¥Examples

function f() {
  return Math.random() < 0.5 ? 42 : 'oops';
}

const z = f() as number;

const items = [1, '2', 3, '4'];

const number = items[0] as number;
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选项​

该规则不可配置。

何时不使用它​

¥When Not To Use It

如果你的代码库有许多不安全的类型断言，则可能很难启用此规则。在项目不安全区域中增加类型安全性时，跳过 no-unsafe-* 规则可能会更容易。你可以考虑在这些特定情况下使用 ESLint 禁用注释，而不是完全禁用此规则。

¥If your codebase has many unsafe type assertions, then it may be difficult to enable this rule. It may be easier to skip the no-unsafe-* rules pending increasing type safety in unsafe areas of your project. You might consider using ESLint disable comments for those specific situations instead of completely disabling this rule.

如果你的项目经常在测试文件中存根对象，则该规则可能会触发大量报告。考虑禁用此类文件的规则以减少频繁警告。

¥If your project frequently stubs objects in test files, the rule may trigger a lot of reports. Consider disabling the rule for such files to reduce frequent warnings.

进一步阅读​

¥Further Reading

Type checked lint rules are more powerful than traditional lint rules, but also require configuring type checked linting.

See Troubleshooting > Linting with Type Information > Performance if you experience performance degradations after enabling type checked rules.

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