Javascript TypeScript 文件中需要“使用严格”？

"Use Strict" needed in a TypeScript file?

提问by DeborahK

I've seen posts regarding where to put the "use strict" line in a TypeScript code file. My question is, why have it at all?

我看过有关在 TypeScript 代码文件中放置“use strict”行的位置的帖子。我的问题是，为什么要拥有它？

Since TypeScript is already a strongly typed language, what does "use strict" add?

既然 TypeScript 已经是强类型语言，那么“use strict”又增加了什么？

采纳答案by David Sherret

Updates

更新

• TypeScript 1.8+: "use strict";is emitted in modules (Read more).
• TypeScript 2.1+: --alwaysStrictcompiler option parses all files in strict mode and emits "use strict"at the top of all outputted files (Read more).

• TypeScript 1.8+："use strict";在模块中发出（阅读更多）。
• TypeScript 2.1+：--alwaysStrict编译器选项以严格模式解析所有文件，并"use strict"在所有输出文件的顶部发出（阅读更多）。

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You can find a list of some examples by searching TypeScript's tests for "in strict mode".

您可以通过在 TypeScript 的“严格模式”测试中搜索一些示例列表。

Here's some examples of code that will only throw a compile time error when you "use strict";:

以下是一些代码示例，它们只会在您执行"use strict";以下操作时引发编译时错误：

// future reserved keyword not allowed as variable name
var let,
    yield,
    public,
    private,
    protected,
    static,
    implements;

// "delete" cannot be called on an identifier
var a;
delete a;

// octal literals not allowed
03;

There are a few more examples where "use strict";would throw an error only at runtime. For example:

还有一些示例"use strict";只会在运行时抛出错误。例如：

"use strict";
delete Object.prototype;

Personally, I don't find it all that useful at preventing me from making mistakes in TypeScript and the additional noise it adds to a file makes me not bother writing it. That said, starting in TS 2.1 I'll enable the --alwaysStrictcompiler option because it adds the slight additional strictness without any code maintenance overhead.

就我个人而言，我认为它对于防止我在 TypeScript 中犯错误并没有多大用处，而且它给文件增加的额外噪音让我懒得写它。也就是说，从 TS 2.1 开始，我将启用--alwaysStrict编译器选项，因为它增加了一些额外的严格性，而没有任何代码维护开销。

回答by Jeremy

For my money, yes, "use strict";should be included in TypeScript files.

对于我的钱，是的，"use strict";应该包含在 TypeScript 文件中。

Disregarding the compile timeeffects of "use strict";on Typescript, there is likely a runtimeimpact when the generated javascript is executed:

不考虑对 Typescript的编译时影响，执行生成的 javascript 时"use strict";可能会影响运行时：

• MDN identifies performance improvementsin avoiding boxing thisin function calls, and the removal of the function.callerand function.argumentsproperties.

• Jeff Walden of Mozilla has also hinted at opportunities for performance gains in this answer.

• MDN 确定了在避免this函数调用中的装箱以及删除function.caller和function.arguments属性方面的性能改进。

• Mozilla 的 Jeff Walden 也在这个答案中暗示了性能提升的机会。