In the sphere of web development, there are multiple ways to upload files when collecting user input. One of the methods is copy-paste. Copy-paste for file input is a very intuitive method of uploading files from users. Copy-paste file input method relieves users of the need to memorize the location of the file they want to upload. In this article, we will discuss how you can implement file input by copy-paste on your website.

We will implement the copy-paste file input by taking advantage of the ClipboadEvent and the EventTarget interfaces. The ClipboardEvent interface provides information about the paste event, and the EventTarget interface allows us to listen to the paste event.

While listening to the paste event, we will attach an event handler function where we decide what to do with the pasted items. In our case, we will take the pasted file and render it instantly after it is completely loaded into the browser. We will begin with the HTML and the styles.

The HTML and the Styles

Let us start by creating the HTML markup of the paste area. The code snippet below is the HTML markup:

    

        Paste your file here
    
    

    

The code snippet above renders a rectangular container within which we will be able to paste files. The container has an attribute called contenteditable set to true. The contenteditable attribute is important to enabling the pasting of files or any other items in the container. If the contenteditable attribute is changed to false or removed, the paste action will not work as expected. We also have a container with the id of preview. We will use the preview container to preview the image pasted by the user.

Let's add a few basic styles to our markup from style.css

*{
    font-family: Arial, Helvetica, sans-serif;
}

body{
    text-align: center;
    margin-block-start: 4rem;
}
#pasteArea {
    border: 2px dashed #ccc;
    padding: 20px;
    width: 300px;
    height: 200px;
    display: flex;
    align-items: center;
    justify-content: center;
    text-align: center;
    cursor: pointer;
    margin: auto;
    color: rgb(5, 89, 89);
}

#preview img {
    max-width: 100%;
    margin-top: 10px;
}

The above markup and style sheet creates a simple dash-bordered container with a simple prompt text as shown in the screenshot below:

Now that we have created the UI, let us add some useful functionalities with JavaScript in the next section.

The Script

In this section, we will use JavaScript to add a paste event listener to the paste area. Before we get the paste area from the DOM to attach the event listener, we first wait for the DOM content to be loaded as in the code snippet below.

document.addEventListener('DOMContentLoaded', () => {
    const pasteArea = document.querySelector('#pasteArea');

    pasteArea.addEventListener('paste', (event) => {

    });
});

In the code snippet above, we have added a listener for the DOMContentLoaded event. This allows us to wait for the DOM tree to be created before we can get the DOM elements. Next, we select the paste area container and append a paste event listener to it.

Getting the file from the pasted items

The paste event handler was left unimplemented in the previous code snippet. Let's implement it by getting the data from the event object and logging them in the console. We will do more with the data later in the article, for now, we just want to ensure that the files are received when items are pasted in the paste area. The code snippet below shows the minimal implementation of the paste event handler.

pasteArea.addEventListener('paste', (event) => {
        const items = event.clipboardData.items
        for (const item of items) {
            if (item.kind === 'file') {
                const file = item.getAsFile()

                console.log(file)
            }
        }
    })

In the code snippet above, we get items from the event.clipboardData object. The event.clipboardData.items is a DataTransferItemList which is a list-like object containing the content of the pasted items. The items are stored in a list because it is possible for a user to copy and paste multiple items at once.

Next, we iterate over the items using the for ...of loop. In the loop, we check if each of the items is a file. If the item is of king 'file', we get it as a file and print it on the browser's console.

Printing the file information on the console is not very useful to the users of your web page. Let's do something a little more interesting in the next section.

Previewing the uploaded file

It would be hard for a user to know that the file upload was successful after pasting the items for the clipboard if we don't show it anywhere. It is important to indicate that the file was successfully uploaded by displaying something that indicates success. What better way to indicate the success of an upload than displaying the uploaded file itself?

In this section, we will extend the paste event handler to create a URL from the received file. We will use the created URL to render the file once it's loaded into the browser. We will take advantage of the FileReader API to create a URL from the file as coded in the snippet below.

pasteArea.addEventListener('paste', (event) => {
        const items = event.clipboardData.items
        for (const item of items) {
            if (item.kind === 'file') {
                const file = item.getAsFile()


                const reader = new FileReader();

                reader.onloadend = (e) => {
                    const url = e.target.result
                    console.log(url)

                };
                reader.readAsDataURL(file);
            }
        }
    });

In the code snippet above, we have created an instance of the FileReader and used it to generate the data URL. We have also appended a loadend event listener to the FileReader object where we log the the result of the reading to the console. This is the first step towards previewing the file, we can now use the URL to display the file.

Assuming the user pasted image files, the following code snippet shows how we can extend the event handler to create a URL and display the image file.

 reader.onloadend = (e) => {
       const url = e.target.result
       const preview = document.querySelector('#preview')
       const img = document.createElement('img');

       img.src = url;
       preview.appendChild(img);
   };

In the code snippet above, we get the preview container from the DOM and create an img element for rendering the image. We assign the created URL as the src of the image and append the image to the preview container. Once the image is appended to the preview container, the user can now know that the image they pasted was successfully loaded into the web page.

Success! We have successfully implemented file uploads by copy-paste on a webpage. This method of file upload gives users the privilege of uploading files easily without the need to click several buttons to select the file to be uploaded. The ClipboadEvent interface provides an easy way to collect data from items pasted on the browser. The FileReader interface allows us to create a URL from the uploaded file and use it to preview the uploaded file.

Feel free to say something in the comment section. Find more about the ClipBoardEvent and the FileReader interfaces from MDN.