为什么一个const必须在打字稿的导出类之外？

问题描述：

这是一个与打字稿范围有关的问题。该listofstuff不变作品，如果它的类右括号外的，但如果它是括号内为什么一个const必须在打字稿的导出类之外？

例如，这个代码不工作：

import {Injectable} from '@angular/core' 

    @Injectable() 
    export class EventListService{ 
    getEvents(){ 
    return listofstuff 
    } 
const listofstuff = [ 
    {name:'Angular Connect', date: '9/26/2036', time: '10am', location: {address: '1 London Rd', city: 'London', country: 'England'}}, 
    {name:'ng-nl', date: '4/15/2037', time: '9am', location: {address: '127 DT ', city: 'Amsterdam', country: 'NL'}}, 
    {name:'ng-conf 2037', date: '4/15/2037', time: '9am', location: {address: 'The Palatial America Hotel', city: 'Salt Lake City', country: 'USA'}}, 
    {name:'UN Angular Summit', date: '6/10/2037', time: '8am', location: {address: 'The UN Angular Center', city: 'New York', country: 'USA'}}, 
] 
}

但这个工程：

import {Injectable} from '@angular/core' 

    @Injectable() 
    export class EventListService{ 
    getEvents(){ 
    return listofstuff 
    } 
} 
const listofstuff = [ 
    {name:'Angular Connect', date: '9/26/2036', time: '10am', location: {address: '1 London Rd', city: 'London', country: 'England'}}, 
    {name:'ng-nl', date: '4/15/2037', time: '9am', location: {address: '127 DT ', city: 'Amsterdam', country: 'NL'}}, 
    {name:'ng-conf 2037', date: '4/15/2037', time: '9am', location: {address: 'The Palatial America Hotel', city: 'Salt Lake City', country: 'USA'}}, 
    {name:'UN Angular Summit', date: '6/10/2037', time: '8am', location: {address: 'The UN Angular Center', city: 'New York', country: 'USA'}}, 
]

来自面向对象的背景（C＃和一些Java），这对我来说很奇怪。有人可以解释这里发生了什么吗？即使在第一个示例中使用“this”关键字也不起作用...

你不能有'const'对象属性（你能吗？） – Pointy

在TypeScript中，[在类范围内]（https://github.com/Microsoft/TypeScript/issues/12），必须使用'只读“而不是”const“。另见https://*.com/questions/46561155/difference-between-const-and-readonly-in-typescript – artem

答

对于类属性，不能使用const关键字。相反，类属性只能标记为public,private,readonly和protected修饰符。

import { Injectable } from '@angular/core' 

@Injectable() 
export class EventListService { 
    readonly listofstuff: any[] = [ 
    { name: 'Angular Connect', date: '9/26/2036', time: '10am', location: { address: '1 London Rd', city: 'London', country: 'England' } }, 
    { name: 'ng-nl', date: '4/15/2037', time: '9am', location: { address: '127 DT ', city: 'Amsterdam', country: 'NL' } }, 
    { name: 'ng-conf 2037', date: '4/15/2037', time: '9am', location: { address: 'The Palatial America Hotel', city: 'Salt Lake City', country: 'USA' } }, 
    { name: 'UN Angular Summit', date: '6/10/2037', time: '8am', location: { address: 'The UN Angular Center', city: 'New York', country: 'USA' } }, 
    ]; 

    getEvents() { 
    return this.listofstuff; 
    } 
}

你会使用this关键字访问listofstuff类属性。 Example

您可以在官方documentation中了解更多关于Typescript类的信息。请记住，默认情况下属性和没有标识符的成员标记为public。从文档：

在TypeScript中，每个成员默认情况下都是公共的。

希望有帮助！

非常有帮助。谢谢！ –

为什么一个const必须在打字稿的导出类之外？

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