Javascript 在Typescript中，类型和接口有什么区别？
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In Typescript, what is the difference between type and interface?
提问by martiansnoop
What are the differences between the following?
以下有什么区别？
type Foo = {
foo: string
};
interface Foo {
foo: string;
}
回答by Ryan Cavanaugh
Interfaces can be extended
接口可以扩展
interface A {
x: number;
}
interface B extends A {
y: string;
}
and also augmented
并且还增加了
interface C {
m: boolean;
}
// ... later ...
interface C {
n: number;
}
Type aliases, however, can represent some things interfaces can't
然而，类型别名可以代表一些接口不能代表的东西
type NumOrStr = number | string;
type NeatAndCool = Neat & Cool;
type JustSomeOtherName = SomeType;
So in general if you just have a plain object type, as shown in your question, an interface is usually a better approach. If you find yourself wanting to write something that can't be written as an interface, or want to just give something a different name, a type alias is better.
所以一般来说，如果你只有一个普通的对象类型，如你的问题所示，接口通常是更好的方法。如果你发现自己想写一些不能写成接口的东西，或者只想给一些东西一个不同的名字，类型别名更好。
回答by Dave Ford
Also, an interface can be implemented.
此外，还可以实现接口。
回答by amit77309
Differences between these too are already in this thread.
这些之间的差异也已经在这个线程中。
type Foo = {
foo: string
};
interface Foo {
foo: string;
}
Here type Fooandinterface Foolooks almost similar so its confusing.
这里type Foo和interface Foo看起来几乎相似，所以它令人困惑。
interfaceis contract that the following properties (herefoo:string) should be there in a object.
interfaceis not class. It is used when language does not support Multiple Inheritance. So interfacecan be a common structure between different classes.
interface约定以下属性（此处foo:string）应存在于对象中。
interface不是class。当语言不支持多重继承时使用它。所以interface可以是不同类之间的公共结构。
class Bar implements Foo {
foo: string;
}
let p: Foo = { foo: 'a string' };
Buttypeand interfaceare used in very different context.
但是type和interface在非常不同的上下文中使用。
let foo: Foo;
let today: Date = new Date();
Here typeof foois Fooand todayis Date.
Its like a variable decleration which holds the information of typeof other variable.
typeis like a superset of interfaces, classes, function signature, other types or even values (like type mood = 'Good' | 'Bad').
At the end typedescribes the possible structure or value of a variable.
这里type的fooisFoo和todayis Date。它就像一个变量声明，它保存了其他变量的类型信息。
type就像接口、类、函数签名、其他类型甚至值（如type mood = 'Good' | 'Bad'）的超集。最后type描述了变量的可能结构或值。
回答by nadav
Types is kinda like Interfaces and vice versa: both can implemented by a class. but there are some important differences: 1. when Type is implemented by a class, the properties which belong to the Type must be initialized inside the class, whereas with Interface they must be declared. 2. as @ryan mentioned : Interface can extend another Interface. Types cannot.
类型有点像接口，反之亦然：两者都可以由类实现。但是有一些重要的区别： 1. 当 Type 由类实现时，属于 Type 的属性必须在类内部初始化，而对于 Interface 它们必须声明。2. 正如@ryan 提到的：接口可以扩展另一个接口。类型不能。
type Person = {
name:string;
age:number;
}
// must initialize all props - unlike interface
class Manager implements Person {
name: string = 'John';
age: number = 55;
// can add props and methods
size:string = 'm';
}
const jane : Person = {
name :'Jane',
age:46,
// cannot add more proprs or methods
//size:'s'
}
回答by Dan
It is wrong to say "Interfaces can be implemented" since types can also be implemented
说“接口可以实现”是错误的，因为类型也可以实现
type A = { a: string };
class Test implements A {
a: string;
}
Although you can do this, you can't implement a type that is a Union of types, which makes totally sense honestly :)
虽然你可以做到这一点，但你不能实现一个类型的联合，老实说这是完全合理的:)
回答by udeep shrestha
type in the typescript is used to reference already existing types. It can not be extended like interface. Examples of typeare:
type 在打字稿中用于引用已经存在的类型。它不能像interface. 例子type有：
type Money = number;
type FormElem = React.FormEvent<HTMLFormElement>;
type Person = [string, number, number];
you can use Rest and Spread in types:
您可以在以下类型中使用 Rest 和 Spread：
type Scores = [string, ...number[]];
let ganeshScore = ["Ganesh", 10, 20, 30]
let binodScore = ["Binod", 10, 20, 30, 40]
Interface, on the other hand, allows you to create a NEW TYPE.
另一方面，界面允许您创建新类型。
interface Person{
name: string,
age: number,
}
Interface can be extended with extends keyword.
interface Todo{
text: string;
complete: boolean;
}
type Tags = [string, string, string]
interface TaggedTodo extends Todo{
tags: Tags
}
