Angular 4 - Persist & retrive variables over session

sessionStore.ts

  persist(key,value){
    /*
     * Store user information in sessionStorage
     * @param {string}  key - key name
     * @param {json}  value - value
     * @return {}
     */
    if(typeof value == "object"){
      return sessionStorage.setItem(key,JSON.stringify(value))
    }else{
      return new Error("Oops! Only Objects can be persisted.")
    }
 }
  retrive(key){
    /*
     * Store user information in sessionStorage
     * @param {string}  key - key name
     * @return {json}
     */
    return  JSON.parse(sessionStorage.getItem(key))
  }