Typescript 接口默认值 | 接口默认值

本文介绍了Typescript 接口默认值的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！

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".

推荐答案

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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