Drag and drop support in JavaScript is probably two to three hundred years old now (plus or minus a few years), but I use it rarely enough such that when I need it, I run over to MDN's article on it as a quick refresher. I thought it might be fun to combine the web's drag and drop support with Adobe's PDF Embed library. Here's what I built.

Support Drag and Drop

Let's begin by just handling drag and drop, not worrying yet about PDF rendering. I began by adding two events to my core Alpine.js div:

<div x-data="app" @drop.prevent="handleDrop" @dragover.prevent>


</div>

You'll notice both a drop event and dragover. Why both? From MDN:

By default, the browser prevents anything from happening when dropping something onto most HTML elements. To change that behavior so that an element becomes a drop zone or is droppable, the element must have both ondragover and ondrop event handler attributes.

We only care about the drop, so dragover just does nothing in this case. Also, note both use .prevent to prevent the default handling of those events by the browser.

In JavaScript, the drop event will have access to the file that was dropped, and with this, we can check for a PDF:

handleDrop(e) {
	let droppedFiles = e.dataTransfer.files;
	if(!droppedFiles) return;
	//only work with file 1
	this.pdfFile = droppedFiles[0];
	if(this.pdfFile.type !== 'application/pdf') return;
	console.log('we got a pdf', this.pdfFile.name);
	// more to come...

Essentially - look for a file (a user could drag and drop multiple) and check the type property to ensure it's a PDF.

And that's it. So how do we get the PDF rendered?

Adding PDF Embed

I've talked about PDF Embed many times here, but if you've never seen it before, you can take a quick look at the Getting Started guide for a review. Basically, include a JavaScript library, figure out what div element will hold the PDF, and then use a few lines of JavaScript to initialize, point to the PDF, and render. Here's a sample of how this would look:

document.addEventListener("adobe_dc_view_sdk.ready", function() {
	var adobeDCView = new AdobeDC.View({clientId: "<YOUR_CLIENT_ID>", divId: "adobe-dc-view"});
    adobeDCView.previewFile(
	{
		content:   {location: {url: "https://acrobatservices.adobe.com/view-sdk-demo/PDFs/Bodea Brochure.pdf"}},
		metaData: {fileName: "Bodea Brochure.pdf"}
	});
});

That's vanilla JavaScript, but how do we use this in Alpine?

First off, notice how the default code listens for an event, adobe_dc_view_sdk.ready. This event is fired when the library is loaded and ready to go. However, you can also check for window.AdobeDC as well. The best solution is to use both - listen for the event and check the window variable.

In Alpine, I used a variable, pdfAPIReady, set to false, and in my init, checked for the window variable:

init() {
	if(window.AdobeDC) this.pdfAPIReady = true;
},

That handles the case of, "The Embed library was ready before Alpine even got started". To handle it not being ready, we can tell Alpine to listen for the adobe_dc_view_sdk.ready event. This brings up two issues:

• It's a document event
• It's an event with a dot in the name

Luckily, Alpine supports that with two directives: .dot.document. Here's how it looks:

<div x-data="app" @drop.prevent="handleDrop" @dragover.prevent @adobe_dc_view_sdk-ready.dot.document="setReady">

Notice I changed the dot in the event to a dash. When Alpine sees the .dot directive, it understands what I really want to listen for. It's absolutely a bit 'wordy', but it works.

Cool. So next I added some UI. This UI will only show up when I'm ready to render events so it makes use of x-show:

<div id="dropBox" x-show="pdfAPIReady">
   <p>
   Please drop your PDF file here...
   </p>
</div>

Now I can return back to my JavaScript code that handles the drop:

handleDrop(e) {
	let droppedFiles = e.dataTransfer.files;
	if(!droppedFiles) return;
	//only work with file 1
	this.pdfFile = droppedFiles[0];
	if(this.pdfFile.type !== 'application/pdf') return;
	console.log('we got a pdf', this.pdfFile.name);

	let reader = new FileReader();
	let name = this.pdfFile.name;

	reader.onloadend = (e) => {
		let filePromise = Promise.resolve(e.target.result);
		this.renderPDF('pdfPreview', filePromise, name);      
	};
	reader.readAsArrayBuffer(this.pdfFile);		
},

After I've checked to ensure I've got a PDF, I use a FileReader object to read the data of the dropped file. This is async and the onloadend handler can then take the final result and pass it to the next function:

renderPDF(div, promise, name) {
	let dcView = new AdobeDC.View({
		clientId: ADOBE_KEY, 
		divId: div
	});

	dcView.previewFile({
		content: { promise: promise }, 
		metaData: { fileName: name }
	});
},

This is a small modification of the default code from the docs, with the big change being using a promise instead of a URL for the source. And that's really all there is.

You can find the complete code below, but you may want to open it up on CodePen to get a bit more 'space' to actually see a PDF.

See the Pen Drag drop to PDF View by Raymond Camden (@cfjedimaster) on CodePen.