To upload file we need a html template. In this template we will create `file input` element that allows to us to choose the file and a button to upload file. To create it open the `App.js` file and update the render function with the below code.

You may notic that we have two method in this `HTML` Fist `fileChangedHandler` and second `submit`

Let's write `fileChangedHandler` function

The `fileChangedHandler` method will called when the user choose file. It will get the file object of selected file and store in the `selectedFile` state.

Now we will write another function which is responsible to upload the file into the server.

import React, { Component } from 'react';
import './App.css';

class App extends Component {
  state =  {
    selectedFile: null,
    imagePreviewUrl: null
  };

  fileChangedHandler = event => {
    this.setState({
      selectedFile: event.target.files[0]
    })

    let reader = new FileReader();
    
    reader.onloadend = () => {
      this.setState({
        imagePreviewUrl: reader.result
      });
    }

    reader.readAsDataURL(event.target.files[0])

  }

  submit = () => {

    var fd = new FormData();

    fd.append('file', this.state.selectedFile);

    var request = new XMLHttpRequest();

    request.onreadystatechange = function() {
      if (this.readyState === 4 && this.status === 200) {
        alert('Uploaded!');
      }
    };
    request.open("POST", "https://us-central1-tutorial-e6ea7.cloudfunctions.net/fileUpload", true);
    request.send(fd);
  }

  render() {

    let $imagePreview = (<div className="previewText image-container">Please select an Image for Preview</div>);
    if (this.state.imagePreviewUrl) {
      $imagePreview = (<div className="image-container" ><img src={this.state.imagePreviewUrl} alt="icon" width="200" /> </div>);
    }

    return (
      <div className="App">
         <input type="file" name="avatar" onChange={this.fileChangedHandler} />
         <button type="button" onClick={this.submit} > Upload </button>
         { $imagePreview }
      </div>
    );
  }
}

export default App;

Our application preview

First we need to create template. In this template we will create file input element that allows to us to choose the file and a button to submit the form. To create it open the app.component.html file and put the below html on it. Instead of app.component.html you can put on another component too!

<div class="container">
    <div class="row">
        <div class="col-md-6 offset-md-3">
            <h3>Choose File</h3>
            <form (ngSubmit)="onSubmit()">
                <div class="form-group">
                    <input type="file" name="image"  />
                </div>
                <div class="form-group">
                    <button class="btn btn-primary">Submit</button>
                </div>
            </form>
        </div>
    </div>
</div>

Configure the HttpClientModule

We will use the Angular 7 HttpClient to upload the file on the server.

So before writing file upload code, first, Open src/app/app.module.ts then add this import.

Add HttpClientModule to imports array under @NgModule

Now open the app.component.ts file and put the below code on it

Here you can see the two methods onSubmit and fileProgress. The fileProgress method will called when the user choose file. It will get the file object of selected file and store in the fileData.

The onSubmit function will called when the form submit. Here we have created a formData object. We will store the file object to the formData and then upload it to the server via Angular 7 HttpClient

After the changes our app.component.ts file will looks like this

Now you can upload the file, But in some case you need more control

Progress Event

If you are dealing with the big file or You may want to show progress to user, Angular 7 httpClient gives you the progress status.

First of all open the app.component.ts file and put the below import

Then you just need to add reportProgress to true and set the observe to events in the config like we have below. You will get all the events on subscribe

Here is the how this looks like