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Angel Hill
Angel Hill

Angular File Download with Progress Indicator using RxJS


How to Create a File Download Progress Bar in Angular 8




Downloading files is a common task for web applications. Whether it's a PDF, ZIP, or any other binary or text-based file, you want to make it accessible and user-friendly for your users. One way to do that is to create a file download progress bar that shows how much of the file has been downloaded and how long it will take to complete.


A file download progress bar can improve the user experience by providing feedback, reducing uncertainty, and increasing trust. It can also prevent users from canceling or interrupting the download process, which can cause errors or data loss.




file download progress bar in angular 8



In this article, you will learn how to create a file download progress bar in Angular 8 using three different options: using a simple HTML link, using HttpClient and RxJS, and using Angular Material Progress Bar. You will also learn the pros and cons of each option and some best practices for creating a file download progress bar in Angular 8.


Option 1: Using a Simple HTML Link




The simplest way to create a file download link in Angular is to use plain HTML with an anchor tag pointing to the file URL with the href attribute. The download attribute informs the browser that it should not follow the link but rather download the URL target. You can also specify its value in order to set the name of the file being downloaded.


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For example, you can create a download link for an archive.zip file like this:


<a href="/downloads/archive.zip" download="archive.zip">archive.zip</a>


You can bind any of these attributes with Angular in order to set the URL and filename dynamically:


<a [href]="download.url" [download]="download.filename"> download.filename </a>


Older browsers, like Internet Explorer, might not recognize the download attribute. For those cases, you can open the download in a new browser tab with the target attribute set to _blank. Make sure though to always include rel="noopener noreferrer" when you're using target="_blank" so you're not opening yourself up to security vulnerabilities.


<a [href]="download.url" target="_blank" rel="noopener noreferrer"> download.filename </a>


If there's no download attribute, the filename for your download will solely depend on the HTTP header Content-Disposition sent by the server that's providing the file. The information from this header might also take precedence even if the download attribute is present.


A link-based solution conforms well to HTML standards and lets the browser do most of the work. However, if you want more control over the download and would like to display some custom progress indicator, you can also download files via Angular's HttpClient.


Option 2: Using HttpClient and RxJS




A file is best represented as a Blob in the browser:


The Blob object represents a A file is best represented as a Blob in the browser:


The Blob object represents a blob, which is a file-like object of immutable, raw data; they can be read as text or binary data, or converted into a ReadableStream so its methods can be used for processing the data.


To download a file as a Blob, you can use the HttpClient service from Angular's common HTTP module. You need to inject it into your component or service and then perform a GET request with the responseType option set to blob:


import HttpClient from '@angular/common/http'; constructor(private http: HttpClient) downloadFile(url: string) return this.http.get(url, responseType: 'blob' );


This will return an Observable that you can subscribe to and get the file data. However, this will not give you any information about the download progress. To get that, you need to use two more options: reportProgress and observe.


The reportProgress option is a boolean that indicates whether or not the HttpClient should track and report the progress of the request. The observe option is a string that specifies what type of events you want to observe. The possible values are body, response, and events. The default value is body, which means you only get the final response body. The response value means you get the full HttpResponse object with headers and status. The events value means you get all the HttpEvents that occur during the request lifecycle, such as sent, upload progress, response header, download progress, and response.


To get the download progress events, you need to set both reportProgress and observe to true and events respectively:


downloadFile(url: string) return this.http.get(url, responseType: 'blob', reportProgress: true, observe: 'events' );


This will return an Observable that you can subscribe to and filter by the HttpEventType.DownloadProgress enum. This event has two properties: loaded and total. The loaded property is the number of bytes that have been downloaded so far. The total property is the total number of bytes to be downloaded, if known. You can use these properties to calculate the percentage of the download progress and display it in your UI.


Once the download is complete, you will get an HttpEventType.Response event with the Blob data in its body property. You can then use the saveAs function from FileSaver.js, a library that implements the HTML5 saveAs() FileSaver interface in browsers that do not natively support it, to save the file to disk. You can also use the filename from the Content-Disposition header or from your own logic.


Here is an example of how to use HttpClient and RxJS to download a file and show its progress:


import Component from '@angular/core'; import HttpClient, HttpEventType from '@angular/common/http'; import saveAs from 'file-saver'; @Component( selector: 'app-download', template: ` <div> <button (click)="downloadFile()">Download</button> <p *ngIf="progress"> progress %</p> </div> ` ) export class DownloadComponent progress: number; constructor(private http: HttpClient) downloadFile() this.http .get('/downloads/archive.zip',


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