Javascript 使用Typescript检查接口类型
这个问题是与这个问题的直接类比 我需要在运行时查明任何类型的变量是否实现了接口。这是我的密码:Javascript 使用Typescript检查接口类型,javascript,typescript,interface,Javascript,Typescript,Interface,这个问题是与这个问题的直接类比 我需要在运行时查明任何类型的变量是否实现了接口。这是我的密码: interface A{ member:string; } var a:any={member:"foobar"}; if(a instanceof A) alert(a.member); 如果在typescript中输入此代码,最后一行将标记为错误,“名称A在当前范围内不存在”。但事实并非如此,该名称确实存在于当前范围中。我甚至可以将变量声明更改为vara:a={member:“foo
interface A{
member:string;
}
var a:any={member:"foobar"};
if(a instanceof A) alert(a.member);
如果在typescript中输入此代码,最后一行将标记为错误,“名称A在当前范围内不存在”。但事实并非如此,该名称确实存在于当前范围中。我甚至可以将变量声明更改为vara:a={member:“foobar”}代码>编辑没有抱怨。在浏览网页并找到另一个问题后,我将接口更改为类,但随后我无法使用对象文本创建实例
我想知道A类型怎么会像那样消失,但看看生成的javascript就可以解释问题了:
var a = {
member: "foobar"
};
if(a instanceof A) {
alert(a.member);
}
没有接口的表示形式,因此不可能进行运行时类型检查
我知道javascript作为一种动态语言没有接口的概念。有没有办法对接口进行类型检查
typescript游乐场的自动完成显示,typescript甚至提供了一个方法实现。如何使用它?您可以在不使用instanceof
关键字的情况下实现您想要的功能,因为您现在可以编写自定义类型的保护:
interface A{
member:string;
}
function instanceOfA(object: any): object is A {
return 'member' in object;
}
var a:any={member:"foobar"};
if (instanceOfA(a)) {
alert(a.member);
}
很多成员
如果需要检查大量成员以确定对象是否与您的类型匹配,则可以添加一个鉴别器。下面是最基本的示例,要求您管理自己的鉴别器。。。您需要深入了解模式,以确保避免重复的鉴别器
interface A{
discriminator: 'I-AM-A';
member:string;
}
function instanceOfA(object: any): object is A {
return object.discriminator === 'I-AM-A';
}
var a:any = {discriminator: 'I-AM-A', member:"foobar"};
if (instanceOfA(a)) {
alert(a.member);
}
您无需使用instanceof
关键字即可实现所需功能,因为您现在可以编写自定义类型的保护:
interface A{
member:string;
}
function instanceOfA(object: any): object is A {
return 'member' in object;
}
var a:any={member:"foobar"};
if (instanceOfA(a)) {
alert(a.member);
}
很多成员
如果需要检查大量成员以确定对象是否与您的类型匹配,则可以添加一个鉴别器。下面是最基本的示例,要求您管理自己的鉴别器。。。您需要深入了解模式,以确保避免重复的鉴别器
interface A{
discriminator: 'I-AM-A';
member:string;
}
function instanceOfA(object: any): object is A {
return object.discriminator === 'I-AM-A';
}
var a:any = {discriminator: 'I-AM-A', member:"foobar"};
if (instanceOfA(a)) {
alert(a.member);
}
我想指出,TypeScript并没有提供直接的机制来动态测试对象是否实现了特定的接口
相反,TypeScript代码可以使用JavaScript技术检查对象上是否存在一组适当的成员。例如:
var obj : any = new Foo();
if (obj.someInterfaceMethod) {
...
}
function foo (arg: number | string) {
if (typeof arg === 'number') {
// fine, type number has toFixed method
arg.toFixed()
} else {
// Property 'toFixed' does not exist on type 'string'. Did you mean 'fixed'?
arg.toFixed()
// TSC can infer that the type is string because
// the possibility of type number is eliminated at the if statement
}
}
interface Dog {
bark: () => void;
}
// The function isDog is a user defined type guard
// the return type: 'pet is Dog' is a type predicate,
// it determines whether the object is a Dog
function isDog(pet: object): pet is Dog {
return (pet as Dog).bark !== undefined;
}
const dog: any = {bark: () => {console.log('woof')}};
if (isDog(dog)) {
// TS now knows that objects within this if statement are always type Dog
// This is because the type guard isDog narrowed down the type to Dog
dog.bark();
}
我想指出,TypeScript并没有提供直接的机制来动态测试对象是否实现了特定的接口
相反,TypeScript代码可以使用JavaScript技术检查对象上是否存在一组适当的成员。例如:
var obj : any = new Foo();
if (obj.someInterfaceMethod) {
...
}
function foo (arg: number | string) {
if (typeof arg === 'number') {
// fine, type number has toFixed method
arg.toFixed()
} else {
// Property 'toFixed' does not exist on type 'string'. Did you mean 'fixed'?
arg.toFixed()
// TSC can infer that the type is string because
// the possibility of type number is eliminated at the if statement
}
}
interface Dog {
bark: () => void;
}
// The function isDog is a user defined type guard
// the return type: 'pet is Dog' is a type predicate,
// it determines whether the object is a Dog
function isDog(pet: object): pet is Dog {
return (pet as Dog).bark !== undefined;
}
const dog: any = {bark: () => {console.log('woof')}};
if (isDog(dog)) {
// TS now knows that objects within this if statement are always type Dog
// This is because the type guard isDog narrowed down the type to Dog
dog.bark();
}
现在可以了,我刚刚发布了一个增强版的TypeScript
编译器,它提供了全反射功能。您可以从类的元数据对象实例化类,从类构造函数检索元数据,并在运行时检查接口/类。你可以去看看
用法示例:
在其中一个typescript文件中,创建一个接口和一个实现该接口的类,如下所示:
interface MyInterface {
doSomething(what: string): number;
}
class MyClass implements MyInterface {
counter = 0;
doSomething(what: string): number {
console.log('Doing ' + what);
return this.counter++;
}
}
现在,让我们打印一些已实现接口的列表
for (let classInterface of MyClass.getClass().implements) {
console.log('Implemented interface: ' + classInterface.name)
}
使用reflec ts编译并启动它:
$ node main.js
Implemented interface: MyInterface
Member name: counter - member kind: number
Member name: doSomething - member kind: function
参见reflection.d.ts了解接口
元类型详细信息
更新:
您可以找到一个完整的工作示例现在可以了,我刚刚发布了一个增强版的TypeScript
编译器,它提供了全反射功能。您可以从类的元数据对象实例化类,从类构造函数检索元数据,并在运行时检查接口/类。你可以去看看
用法示例:
在其中一个typescript文件中,创建一个接口和一个实现该接口的类,如下所示:
interface MyInterface {
doSomething(what: string): number;
}
class MyClass implements MyInterface {
counter = 0;
doSomething(what: string): number {
console.log('Doing ' + what);
return this.counter++;
}
}
现在,让我们打印一些已实现接口的列表
for (let classInterface of MyClass.getClass().implements) {
console.log('Implemented interface: ' + classInterface.name)
}
使用reflec ts编译并启动它:
$ node main.js
Implemented interface: MyInterface
Member name: counter - member kind: number
Member name: doSomething - member kind: function
参见reflection.d.ts了解接口
元类型详细信息
更新:
您可以在TypeScript 1.6中找到一个完整的工作示例,它将完成这项工作
interface Foo {
fooProperty: string;
}
interface Bar {
barProperty: string;
}
function isFoo(object: any): object is Foo {
return 'fooProperty' in object;
}
let object: Foo | Bar;
if (isFoo(object)) {
// `object` has type `Foo`.
object.fooProperty;
} else {
// `object` has type `Bar`.
object.barProperty;
}
正如Joe Yang提到的:自从TypeScript 2.0以来,您甚至可以利用标记的联合类型
interface Foo {
type: 'foo';
fooProperty: string;
}
interface Bar {
type: 'bar';
barProperty: number;
}
let object: Foo | Bar;
// You will see errors if `strictNullChecks` is enabled.
if (object.type === 'foo') {
// object has type `Foo`.
object.fooProperty;
} else {
// object has type `Bar`.
object.barProperty;
}
它也可以与开关一起工作。在TypeScript 1.6中,将完成这项工作
interface Foo {
fooProperty: string;
}
interface Bar {
barProperty: string;
}
function isFoo(object: any): object is Foo {
return 'fooProperty' in object;
}
let object: Foo | Bar;
if (isFoo(object)) {
// `object` has type `Foo`.
object.fooProperty;
} else {
// `object` has type `Bar`.
object.barProperty;
}
正如Joe Yang提到的:自从TypeScript 2.0以来,您甚至可以利用标记的联合类型
interface Foo {
type: 'foo';
fooProperty: string;
}
interface Bar {
type: 'bar';
barProperty: number;
}
let object: Foo | Bar;
// You will see errors if `strictNullChecks` is enabled.
if (object.type === 'foo') {
// object has type `Foo`.
object.fooProperty;
} else {
// object has type `Bar`.
object.barProperty;
}
它也可以与开关一起工作。typescript 2.0
typescript 2.0引入带标记的联合
用户定义的类型保护怎么样
接口鸟{
苍蝇();
layEggs();
}
界面鱼{
游泳();
layEggs();
}
函数是鱼(宠物:鱼|鸟):宠物是鱼{//魔法发生在这里
返回(宠物)。游泳!==未定义;
}
//现在“游泳”和“飞”都可以了。
如果(鱼(宠物)){
宠物游泳;
}
否则{
pet.fly();
}
用户定义的类型防护怎么样
接口鸟{
苍蝇();
layEggs();
}
界面鱼{
游泳();
layEggs();
}
函数是鱼(宠物:鱼|鸟):宠物是鱼{//魔法发生在这里
返回(宠物)。游泳!==未定义;
}
//现在“游泳”和“飞”都可以了。
如果(鱼(宠物)){
宠物游泳;
}
否则{
pet.fly();
}
打字保护装置
interface MyInterfaced {
x: number
}
function isMyInterfaced(arg: any): arg is MyInterfaced {
return arg.x !== undefined;
}
if (isMyInterfaced(obj)) {
(obj as MyInterfaced ).x;
}
打字机
interface MyInterfaced {
x: number
}
function isMyInterfaced(arg: any): arg is MyInterfaced {
return arg.x !== undefined;
}
if (isMyInterfaced(obj)) {
(obj as MyInterfaced ).x;
}
这里还有另一个选项:模块提供了一个构建时工具,可以将TypeScript接口转换为运行时描述符,并可以检查对象是否满足它
以OP为例,
首先运行ts interface builder
,它会生成一个新的简明文件,其中包含一个描述符,例如foo ti.ts
,您可以这样使用它:
从“/foo ti.ts”导入fooDesc;
从“ts接口检查器”导入{createCheckers};
const{A}=createCheckers(fooDesc);
检查({成员:“你好”});//好啊
检查({成员:17});//因“.成员不是字符串”而失败
你可以创造
declare const isCompositeFilterDescriptor: (source: FilterDescriptor | CompositeFilterDescriptor) => source is CompositeFilterDescriptor;
const filters: Array<FilterDescriptor | CompositeFilterDescriptor> = filter.filters;
filters.forEach((element: FilterDescriptor | CompositeFilterDescriptor) => {
if (isCompositeFilterDescriptor(element)) {
// element type is CompositeFilterDescriptor
} else {
// element type is FilterDescriptor
}
});
function foo (arg: number | string) {
if (typeof arg === 'number') {
// fine, type number has toFixed method
arg.toFixed()
} else {
// Property 'toFixed' does not exist on type 'string'. Did you mean 'fixed'?
arg.toFixed()
// TSC can infer that the type is string because
// the possibility of type number is eliminated at the if statement
}
}
interface Dog {
bark: () => void;
}
// The function isDog is a user defined type guard
// the return type: 'pet is Dog' is a type predicate,
// it determines whether the object is a Dog
function isDog(pet: object): pet is Dog {
return (pet as Dog).bark !== undefined;
}
const dog: any = {bark: () => {console.log('woof')}};
if (isDog(dog)) {
// TS now knows that objects within this if statement are always type Dog
// This is because the type guard isDog narrowed down the type to Dog
dog.bark();
}
// Notice there is no naming conflict, because interfaces are a *type*
export const IAnimal = Symbol("IAnimal");
export interface IAnimal {
[IAnimal]: boolean; // the fubber
}
export const IDog = Symbol("IDog");
export interface IDog extends IAnimal {
[IDog]: boolean;
}
export const IHound = Symbol("IDog");
export interface IHound extends IDog {
// The fubber can also be typed as only 'true'; meaning it can't be disabled.
[IDog]: true;
[IHound]: boolean;
}
import { IDog, IAnimal } from './interfaces';
class Dog implements IDog {
// Multiple fubbers to handle inheritance:
[IAnimal] = true;
[IDog] = true;
}
class Hound extends Dog implements IHound {
[IHound] = true;
}
import { IDog, IAnimal } from './interfaces';
let dog = new Dog();
if (dog instanceof Hound || dog[IHound]) {
// false
}
if (dog[IAnimal]?) {
// true
}
let houndDog = new Hound();
if (houndDog[IDog]) {
// true
}
if (dog[IDog]?) {
// it definitely is a dog
}