部分 T仅适用于内联值 [英] Partial<T> only works with inline values

问题描述

为什么下面的代码表现得像它一样?它是 TypeScript 编译器中的错误还是缺失的功能?

Why does the code below behave like it does? Is it a bug in the TypeScript compiler or missing feature?

class MyType {
  constructor(public readonly value1: string, public readonly value2: number) {
  }  
}

function myFunction(props: Partial<MyType>): void {
  // Do something here    
}

myFunction({ }); // Compiles
myFunction({ value1: 'string', value2: 42 }); // Compiles
myFunction({ wrongValue: true }); // Compile error!!

const myValue1 = {};
const myValue2 = { value1: 'string', value2: 42 };
const myValue3 = { wrongValue: true };

myFunction(myValue1); // Compiles
myFunction(myValue2); // Compiles
myFunction(myValue3); // Compiles, but why?!? I expected this not to compile!

我使用的是 TypeScript 2.1.6 版

I used TypeScript version 2.1.6

推荐答案

您要的是精确类型，已跟踪 这里.

What you are asking for is exact type, which is tracked here.

目前 TypeScript 只会检查对象字面量的过多对象键，主要是检查错字.将对象绑定到变​​量后，TypeScript 不会检查过多的键.

Currently TypeScript will only check excessive object keys for object literal, mainly for typo. After you bind a object to variable, TypeScript will not check excessive keys.

规范:https://github.com/Microsoft/TypeScript/blob/02547fe664a1b5d1f07ea459f054c34e356d3746/doc/spec.md#3115-excess-properties

Partial 有效地为类的字段添加了可选标记.

Partial is effectively add optional mark to the fields of your class.

因此它不会为 myValue3 报告错误.

So it does not report error for myValue3.

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