在TypeScript类中,可以为属性声明类型,例如:

class className {
  property: string;
};

如何在对象文字中声明属性的类型?

我已经尝试了以下代码,但它不能编译:

var obj = {
  property: string;
};

我得到以下错误:

名称“string”在当前作用域中不存在

是我做错了什么还是这是个bug?


当前回答

在TypeScript中,如果我们声明object,那么我们将使用以下语法:

[access modifier] variable name : { /* structure of object */ }

例如:

private Object:{ Key1: string, Key2: number }

其他回答

你已经很接近了,你只需要用a:替换=。您可以使用对象类型文字(参见规范第3.5.3节)或接口。使用对象类型文字接近于你所拥有的:

var obj: { property: string; } = { property: "foo" };

但是你也可以使用接口

interface MyObjLayout {
    property: string;
}

var obj: MyObjLayout = { property: "foo" };
// Use ..

const Per = {
  name: 'HAMZA',
  age: 20,
  coords: {
    tele: '09',
    lan: '190'
  },
  setAge(age: Number): void {
    this.age = age;
  },
  getAge(): Number {
    return age;
  }
};
const { age, name }: { age: Number; name: String } = Per;
const {
  coords: { tele, lan }
}: { coords: { tele: String; lan: String } } = Per;

console.log(Per.getAge());

用DRY将对象文字转换为类型

只做:

const myObject = {
   hello: 'how are you',
   hey: 'i am fine thank you'
}
type myObjectType = keyof typeof MyObject

完成工作!

你可以使用预定义的实用程序类型Record<Keys, type >:

const obj: Record<string, string> = {
  property: "value",
};

它允许为你的对象文字指定键:

type Keys = "prop1" | "prop2"

const obj: Record<Keys, string> = {
  prop1: "Hello",
  prop2: "Aloha",
  something: "anything" // TS Error: Type '{ prop1: string; prop2: string; something: string; }' is not assignable to type 'Record<Keys, string>'.
                        //   Object literal may only specify known properties, and 'something' does not exist in type 'Record<Keys, string>'.
};

属性值的类型:

type Keys = "prop1" | "prop2"
type Value = "Hello" | "Aloha"

const obj1: Record<Keys, Value> = {
  prop1: "Hello",
  prop2: "Hey", // TS Error: Type '"Hey"' is not assignable to type 'Value'.
};

要小心了。这对一些人来说可能是显而易见的,但类型声明:

const foo: TypeName = {}

与as的铸造相比不一样:

const foo = {} as TypeName

尽管有人建议把它用在其他答案上。

例子:

谢谢,类型安全!:

const foo: { [K in 'open' | 'closed']: string } = {}
// ERROR: TS2739: Type '{}' is missing the following properties from type '{ open: string; closed: string; }': open, closed

再见,类型安全!:

const foo = {} as { [K in 'open' | 'closed']: string }
// No error