Check if download is finished in angular 5

I am using Angular 5 and Angular5csv for exporting csv, I want to detect if the downloaded file is finish downloading so that I can add success message, how can I achieve that?

Here is my code in generating csv file:

downloadReport(reportName){
    this.reports = [];
    this.loadReport = true;
    this.data.getReports(rosterId,reportName)
        .subscribe((data:any)=>{
            var report = data.value.toString().replace(/['"]+/g, '').split('\n');
            for (let index = 0; index < report.length; index++) {
                this.reports[index] = report[index].split(',');
            }
            this.loadReport = false;
            new Angular5Csv(this.reports,reportName.replace("_",' '));
            this.logger.success("Success","Downloaded report successfully."); // Add success message here after download
        },()=>{
            this.logger.error("Error","An error occured while processing your request.");
            this.loadReport = false;
        });
}