Typescript class which has only the constants

I would like to keep my cache keys in a central place.I would like to do it as a constant file.At this moment I have declared cache keys each and every page where it's required.But I need to remove that duplication.How can I do that?

One of cache key declaration:

purchasedOfflineArticlesKey: string = 'myLibraryPurchasedOfflineArticles';

Can you tell me a proper design for this? Do I need to create a class for this and use that class in other places where it needs or any other way? Hope you'll give feedback for this.

Update:

I have cache service like below.

local-cache-service.ts

import { Injectable } from '@angular/core';
import { CacheService } from "ionic-cache";

@Injectable()
export class LocalCacheServiceProvider {

  constructor(private cache: CacheService) { }

  //get Item
  getItem(key: string): Promise<any> {
    return this.cache.getItem(key);
  }
}

I have used it like this:

offline-articles.ts

private purchasedOfflineArticlesKey: string = 'myLibraryPurchasedOfflineArticles';

 constructor(private localCacheService: LocalCacheServiceProvider) {
  }

     ionViewDidLoad() {
        this.localCacheService.getItem(this.purchasedOfflineArticlesKey).then(values => {
          this.arrangeMyOfflineArticles(values);
        }).catch(reason => {
        });
      }