I want to allow users to drag images from their desktop onto a browser window and then upload those images to a server. I want to upload each file only once, even if it is dropped on the window several times. For security reasons, the information from File object that is accessible to JavaScript is limited. According to msdn.microsoft.com, only the following properties can be read:
namelastModifiedDate
(Safari also exposes size and type).
The user can drop two images with the same name and last modified date from different folders onto the browser window. There is a very small but finite chance that these two images are in fact different.
I've created a script that reads in the raw dataURL of each image file, and compares it to files that were previously dropped on the window. One advantage of this is that it can detect identical files with different names.
This works, but it seems overkill. It also requires a huge amount of data to be stored. I could improve this (and add to the overkill) by making a hash of the dataURL, and storing that instead.
I'm hoping that there may be a more elegant way of achieving my goal. What can you suggest?
<!DOCTYPE html>
<html>
<head>
<title>Detect duplicate drops</title>
<style>
html, body {
width: 100%;
height: 100%;
margin: 0;
background: #000;
}
</style>
<script>
var body
var imageData = []
document.addEventListener('DOMContentLoaded', function ready() {
body = document.getElementsByTagName("body")[0]
body.addEventListener("dragover", swallowEvent, false)
body.addEventListener("drop", treatDrop, false)
}, false)
function swallowEvent(event) {
// Prevent browser from loading the dropped image in an empty page
event.preventDefault()
event.stopPropagation()
}
function treatDrop(event) {
swallowEvent(event)
for (var ii=0, file; file = event.dataTransfer.files[ii]; ii++) {
importImage(file)
}
}
function importImage(file) {
var reader = new FileReader()
reader.onload = function fileImported(event) {
var dataURL = event.target.result
var index = imageData.indexOf(dataURL)
var img, message
if (index < 0) {
index = imageData.length
console.log(dataURL)
imageData.push(dataURL, file.name)
message = "Image "+file.name+" imported"
} else {
message = "Image "+file.name+" imported as "+imageData[index+1]
}
img = document.createElement("img")
img.src = imageData[index] // copy or reference?
body.appendChild(img)
console.log(message)
}
reader.readAsDataURL(file)
}
</script>
</head>
<body>
</body>
</html>
file.sizeis well supported, so you can lower the odds more without any file data handling. – Haigh