[英]What does {} mean in TypeScript?
I am guessing it means empty object, but not sure...我猜这意味着空对象,但不确定......
I can't find that type on https://www.typescriptlang.org/docs/handbook/basic-types.html .我在https://www.typescriptlang.org/docs/handbook/basic-types.html上找不到这种类型。
interface Component<P = {}, S = {}, SS = any> extends ComponentLifecycle<P, S, SS> { }
The type {}
does not exactly mean an "empty object", because other types of object - which may not be empty - are assignable to the type {}
.类型{}
并不完全意味着“空对象”,因为其他类型的对象 - 可能不是空的 - 可以分配给类型{}
。 For example:例如:
function acceptsEmpty(obj: {}): void {
console.log(obj);
}
let notEmpty: {a: string} = {a: 'test'};
// no error; {a: string} is asssignable to {}
acceptsEmpty(notEmpty);
So essentially, the type {}
means "not required to have any properties, but may have some", and likewise the type {a: string}
means "must have a property named a
whose value is a string
, but may have other properties too".所以本质上,类型{}
表示“不需要有任何属性,但可能有一些”,同样类型{a: string}
表示“必须有一个名为a
的属性,其值为string
,但可能有其他属性也”。
So {}
imposes almost no constraints on its values;因此, {}
对其值几乎没有任何限制; the only rule is that it can't be null
or undefined
.唯一的规则是它不能为null
或undefined
。 It is similar to the type object
in this regard, except that object
also forbids primitive values, while {}
allows them:在这方面它类似于类型object
,除了object
也禁止原始值,而{}
允许它们:
// no error
let anything: {} = 1;
// error: Type '1' is not assignable to type 'object'.
let noPrimitivesAllowed: object = 1;
Component<P = {}, S = {}, SS = any>
means that the default types for P and S are empty objects. Component<P = {}, S = {}, SS = any>
表示 P 和 S 的默认类型是空对象。
So you can use the interface with 0..3 generic params like so:因此,您可以使用具有 0..3 通用参数的接口,如下所示:
const a: Component // = Component<{},{},any>
const b: Component<SomeType> // = Component<Some,{},any>
const c: Component<SomeType, SomeOtherType> // = Component<SomeType, SomeOtherType, any>
const d: Component<SomeType, SomeOtherType, []> // = Component<SomeType, SomeOtherType, []>
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