How to use the msal.Constants.errorDescription function in msal

private processRedirectCallBack(hash: string): void {
        this._logger.info('Processing the callback from redirect response');
        const requestInfo = this.getRequestInfo(hash);
        const token = requestInfo.parameters[Constants.accessToken] || requestInfo.parameters[Constants.idToken];
        const errorDesc = requestInfo.parameters[Constants.errorDescription];
        const error = requestInfo.parameters[Constants.error];
        var tokenType: string;
        this._cacheStorage.removeItem(Constants.urlHash);
        var msalError = new MSALError(error, errorDesc);
        var authenticationResult = new AuthenticationResult(token);
        if (requestInfo.parameters[Constants.accessToken]) {
            tokenType = Constants.accessToken;
            if (token) {
                authenticationResult.tokenType= tokenType;
                this.broadcastService.broadcast("msal:acquireTokenSuccess", authenticationResult);
            }
            else if (error && errorDesc) {
                //TODO this should also send back the scopes
                this.broadcastService.broadcast("msal:acquireTokenFailure", msalError);
            }
        }

processRedirectCallBack(hash) {
        this._logger.info('Processing the callback from redirect response');
        const requestInfo = this.getRequestInfo(hash);
        const token = requestInfo.parameters[Constants.accessToken] || requestInfo.parameters[Constants.idToken];
        const errorDesc = requestInfo.parameters[Constants.errorDescription];
        const error = requestInfo.parameters[Constants.error];
        var tokenType;
        this._cacheStorage.removeItem(Constants.urlHash);
        var msalError = new MSALError(error, errorDesc);
        var authenticationResult = new AuthenticationResult(token);
        if (requestInfo.parameters[Constants.accessToken]) {
            tokenType = Constants.accessToken;
            if (token) {
                authenticationResult.tokenType = tokenType;
                this.broadcastService.broadcast("msal:acquireTokenSuccess", authenticationResult);
            }
            else if (error && errorDesc) {
                //TODO this should also send back the scopes
                this.broadcastService.broadcast("msal:acquireTokenFailure", msalError);
            }
        }