为什么const必须在typescript中的export类之外？

Question

Here is a question relating to scope in typescript. The listofstuff constant works if it outside of the class closing bracket, but not if it is inside the bracket

for instance, this code does not work:

  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'}},
]
}

But this works:

 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'}},
]

Coming from an object oriented background (C# and some java), this is strange to me. can someone explain what is going on here? Even using the "this" keyword in the first example does not work...

Answer 1

You cannot use the const keyword for class properties. Instead class properties can only be marked with public , private , readonly and protected modifiers.

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;
  }
}

You'd access the listofstuff class property using the this keyword. Example

You can read more about Typescript classes in the official documentation . Keep in mind properties and members without an identifier are marked as public by default. From the documentation:

In TypeScript, each member is public by default.

Hopefully that helps!