How to use the nem2-sdk.TransactionHttp function in nem2-sdk

exports.announce = (url, tx, ...subscriber) => {
  const transactionHttp = new nem.TransactionHttp(url)
  const subscription = transactionHttp.announce(tx)
  announceUtil(subscription, url, tx, ...subscriber)
}

public constructor(url: string) {
    this.transactionHttp = new TransactionHttp(url);
    this.accountHttp = new AccountHttp(url);
    this.listener = new Listener(url);
  }

public getTransactionById(transactionID: string, urls?: string): Observable {
        let transactionHttp: TransactionHttp;
        if (urls) {
            transactionHttp = new TransactionHttp(urls);
        } else {
            if (this.publicAccount.address.networkType === NetworkType.MIJIN) {
                throw new Error(Errors[Errors.MIJIN_ENDPOINT_NEEDED]);
            }
            transactionHttp = new TransactionHttp(HistoricalEndpoints[this.publicAccount.address.networkType]);
        }
        return transactionHttp.getTransaction(transactionID);
    }

public getTransactionById(transactionID: string, urls?: string): Observable {
        let transactionHttp: TransactionHttp;
        if (urls) {
            transactionHttp = new TransactionHttp(urls);
        } else {
            if (this.publicAccount.address.networkType === NetworkType.MIJIN) {
                throw new Error(Errors[Errors.MIJIN_ENDPOINT_NEEDED]);
            }
            transactionHttp = new TransactionHttp(HistoricalEndpoints[this.publicAccount.address.networkType]);
        }
        return transactionHttp.getTransaction(transactionID);
    }