file-upload-input Is an Angular Component

Athwart File Upload

We volition know that how to create a functional Angular file upload component that requires a file of a given extension to be uploaded and sends the file to the backend via an HTTP Post call.

The custom component will have an upload loading indicator and will support upload cancellation. We will requite an case (in Node) of treatment a file in the backend.

How to Upload Files to the Browser

To create an Angular file upload component, we beginning demand to understand how to upload files in plain HTML and JavaScript and take it from at that place.

The main component for uploading files to the browser is a plainly HTML input of the file type:

This input will allow the user to open the browser file selection dialog and select one or more files (by default). Hither'due south what the input looks like:

Y'all can select a file from file input box, and then with a footling JavaScript, you can transport information technology to the backend.

Why don't we see file input often?

The problem with this plain file input is that it's very difficult to manner by default. Some applied styles tin't exist changed, and we can't even change the text on the button!

It is the default browser behavior that cannot be changed and is the reason why we don't see this plain file input on the interfaces we use daily, like Gmail, etc.

Because it is impossible to style this file input properly, the near mutual option is never to show it to the end-user.

How does the input of type file work?

When the user selects a file using the file upload dialog, an event of type

The change will be emitted. The event volition so comprise the list of files the user has selected on the target.

Here is the output nosotros see on the console afterwards the user selects the file:

{   lastModified: 1601984029839   lastModifiedDate: Tue Oct 06 2020 13:33:49 GMT+0200 (Central European Summertime Time)    name: "angular-forms-course-small.jpg"   size: 56411   type: "image/jpeg"   webkitRelativePath: "" }

When the change event is triggered, the browser's file is not automatically uploaded to the backend. Instead, nosotros'll need to trigger an HTTP asking ourselves in response to the alter effect.

Creating the User Interface of the File Upload Component

It is incommunicable to properly mode a patently input of a file, we hide it from the user and then build an alternate file upload UI that uses the file input behind the scenes.

Template for the initial file upload component:

The user interface is divided into two different parts. At the pinnacle, we have a plainly file input, which is used to open the file upload dialog and handle the change event.

This plain input text is hidden from the user, as nosotros can see in the component CSS:

We take the file-upload container div, which contains the actual UI that the user can see on the screen.

For example, we built this UI with Angular Material components, but of course, the optional file upload UI can take whatever form you like.

This UI tin can be a dialog, a drag and drop zone, or, as in the example of our component, simply a styled push button:

Notice in the component template how the upload blue button and the invisible file input are continued. When the user clicks the blueish button, a click handler triggers the file input via fileUpload.click().

The user would then select a file from the file upload dialog, and the modify event would be triggered and handled by onFileSelected().

Uploading file to backend using Athwart HTTP customer

Now let's take a wait at our component class and implementation onFileSelected():

Here is the component:

We are getting a reference to the files that the user has selected by accessing events. Target. Files holding.

So nosotros create the form payload using the FormData API. It is a standard browser API and is non Angular-specific.

Nosotros utilize the Athwart HTTP client to brand HTTP requests and transport the file to the backend.

At this betoken, we will already have a working file upload component.

How to brandish file upload progress indicator

We are adding a few more than elements to the UI of our file upload component. Here is the file upload component template:

The 2 main elements we've added to the UI are:

An Angular Material progress bar, which is visible only when the file upload is still in progress.
An Upload Cancel push, besides visible only if an upload is still in progress

How practice you know how much file has been uploaded?

We implement the progress indicator by using the written report progress characteristic of the Angular HTTP client.

With this feature, nosotros can become notified of the progress of file uploads through multiple events emitted by HTTP Observables.

To come across this in action, allow's accept a wait at the last version of the FileUpload component class, which has all its features implemented:

Every bit nosotros can see, we have set the ReportProgress holding to true in our HTTP call, and nosotros have also set up the Overview property in the Value issue.

We will receive an upshot object reporting the progress of the HTTP request.

These events will be emitted as the value of http$observable and come in different types:

Upload Progress type events report the percentage of a file that has already been uploaded.
Events of the type Feedback report that the upload is consummate
By using events of type UploadProgress, we are saving the ongoing upload per centum in a member variable UploadProgress, which nosotros utilise to update the value of the progress indicator bar.
When the upload completes or fails, we demand to hide the progress bar from the user.

We tin can be certain to do this past using the RxJs finalize operator, which will call the reset() method in both cases: upload success or failure.

How to cancel an ongoing file upload

To support file upload cancellation, we must refer to the RxJs subscription object when the http$appreciable is subscribed.

In our component, we shop this membership object in the uploadSub member variable.

While the upload is nevertheless in progress, the user tin abolish it past clicking the Cancel push. Then the cancelUpload() upload method is invoked, and the HTTP request can be canceled by unsubscribing from the UploadSub subscription.

Canceling this subscription will immediately cancel the ongoing file upload.

How to accept certain type of files

In the final version of our file upload component, we can require the user to upload a certain type of file using the required file blazon property:

This holding is passed to the file input'southward take property in the file upload template, forcing the user to select a PNG file from the file upload dialog.

How to Upload Multiple Files

The browser file selection dialog volition allow the user to select just one file to upload by default.

But by using the Multiple backdrop, nosotros can allow the user to select multiple files:

Notation that this volition crave a complete dissimilar UI than the ane nosotros created. A mode upload push button with a progress indicator works well for uploads of merely one file.

For a multi-file upload scenario, various UIs can be created: a floating dialog with the upload progress of all files, etc.

Treatment uploaded file on node backend.

The way y'all handle an uploaded file in your backend depends on the technology you use, only let's give a quick instance of how to do it using the Node and Express frameworks.

We need to install the express-fileupload packet first. And then nosotros can add this package as middleware to our express application:

We have to do is define an express route to handle file upload requests:

Summary

The best way to handle file uploads in Athwart is to build i or more than custom components based on the supported upload scenarios.

The file upload component must comprise an HTML input type file that allows users to select 1 or more files from the file system.

This file input is hidden from the user as it is not stylable and should be replaced past a more user-friendly UI.

By using the file input in the background, nosotros tin refer to the file through the alter upshot, which we can then utilize to make an HTTP request and ship the file to the backend.

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Source: https://www.javatpoint.com/angular-file-upload