Typescript 接口默认值 [英] Typescript interface default values

问题描述

我在 TypeScript 中有以下接口:

I have the following interface in TypeScript:

interface IX {
    a: string,
    b: any,
    c: AnotherType
}

我声明了一个该类型的变量并初始化了所有属性

I declare a variable of that type and I initialize all the properties

let x: IX = {
    a: 'abc',
    b: null,
    c: null
}

然后我稍后在 init 函数中为它们分配实际值

Then I assign real values to them in an init function later

x.a = 'xyz'
x.b = 123
x.c = new AnotherType()

但我不喜欢在声明对象时必须为每个属性指定一堆默认的空值，因为它们稍后将被设置为实际值.我可以告诉界面将我不提供的属性默认为 null 吗?什么会让我这样做:

But I don't like having to specify a bunch of default null values for each property when declaring the object when they're going to just be set later to real values. Can I tell the interface to default the properties I don't supply to null? What would let me do this:

let x: IX = {
    a: 'abc'
}

没有得到编译器错误.现在它告诉我

without getting a compiler error. Right now it tells me

TS2322:类型{}"不可分配给类型'九'.类型{}"中缺少属性b".

TS2322: Type '{}' is not assignable to type 'IX'. Property 'b' is missing in type '{}'.

推荐答案

我可以告诉接口将我不提供的属性默认为 null 吗?什么会让我这样做

Can I tell the interface to default the properties I don't supply to null? What would let me do this

没有.你不能为接口或类型别名提供默认值，因为它们只是编译时，默认值需要运行时支持

No. You cannot provide default values for interfaces or type aliases as they are compile time only and default values need runtime support

但未指定的值在 JavaScript 运行时默认为 undefined.所以你可以将它们标记为可选:

But values that are not specified default to undefined in JavaScript runtimes. So you can mark them as optional:

interface IX {
  a: string,
  b?: any,
  c?: AnotherType
}

现在当你创建它时你只需要提供a:

And now when you create it you only need to provide a:

let x: IX = {
    a: 'abc'
};

您可以根据需要提供值:

You can provide the values as needed:

x.a = 'xyz'
x.b = 123
x.c = new AnotherType()

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