TypeScript Strict Mode 防止的五类运行时事故

TypeScript Strict Mode 不是风格选择，而是把缺失值、any 扩散、危险索引、模糊函数契约和未验证 JSON 提前暴露的安全网。外部数据应从 unknown 开始，在边界验证必要字段，再转换成稳定的内部模型。

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1. null 和 undefined

TypeScript Strict Mode 不是风格选择，而是把缺失值、any 扩散、危险索引、模糊函数契约和未验证 JSON 提前暴露的安全网。外部数据应从 unknown 开始，在边界验证必要字段，再转换成稳定的内部模型。 The practical rule is to decide behavior before runtime: empty state, fallback value, controlled error, or validated model. This keeps reviews focused and prevents hidden assumptions from reaching users.

2. any 扩散

TypeScript Strict Mode 不是风格选择，而是把缺失值、any 扩散、危险索引、模糊函数契约和未验证 JSON 提前暴露的安全网。外部数据应从 unknown 开始，在边界验证必要字段，再转换成稳定的内部模型。 The practical rule is to decide behavior before runtime: empty state, fallback value, controlled error, or validated model. This keeps reviews focused and prevents hidden assumptions from reaching users.

3. 危险索引

TypeScript Strict Mode 不是风格选择，而是把缺失值、any 扩散、危险索引、模糊函数契约和未验证 JSON 提前暴露的安全网。外部数据应从 unknown 开始，在边界验证必要字段，再转换成稳定的内部模型。 The practical rule is to decide behavior before runtime: empty state, fallback value, controlled error, or validated model. This keeps reviews focused and prevents hidden assumptions from reaching users.

4. 函数契约

TypeScript Strict Mode 不是风格选择，而是把缺失值、any 扩散、危险索引、模糊函数契约和未验证 JSON 提前暴露的安全网。外部数据应从 unknown 开始，在边界验证必要字段，再转换成稳定的内部模型。 The practical rule is to decide behavior before runtime: empty state, fallback value, controlled error, or validated model. This keeps reviews focused and prevents hidden assumptions from reaching users.

5. 未验证 JSON

TypeScript Strict Mode 不是风格选择，而是把缺失值、any 扩散、危险索引、模糊函数契约和未验证 JSON 提前暴露的安全网。外部数据应从 unknown 开始，在边界验证必要字段，再转换成稳定的内部模型。 The practical rule is to decide behavior before runtime: empty state, fallback value, controlled error, or validated model. This keeps reviews focused and prevents hidden assumptions from reaching users.

Rollout checklist

• Enable strict in a branch and group errors by risk.
• Start with null handling and external data boundaries.
• Replace implicit any with unknown plus validation.
• Add explicit return types to public functions.
• Keep temporary casts visible until they are removed.

FAQ

Does Strict Mode slow development?

During migration it can, but it reduces production rework by exposing shape and contract errors earlier.

Is optional chaining enough?

No. It prevents one crash but does not decide the user experience when data is missing.

Do schema libraries matter?

Small boundaries can use handwritten guards. Larger products benefit from shared schemas.