Uploading a png to imgur using javascript

Question

I'm trying to use Javascript to upload a png to imgur. I've used the code directly from the Imgur API example, but I don't think I am passing the png file properly as I get an error message saying file.type is undefined. I think the file is ok as I've tried this with a few different pngs. My code is as follows:

<html>
<head>
<script type="text/javascript">
function upload(file) {
   // file is from a <input> tag or from Drag'n Drop
   // Is the file an image?
   if (!file || !file.type.match(/image.*/)) return;

   // It is!
   // Let's build a FormData object
   var fd = new FormData();
   fd.append("image", file); // Append the file
   fd.append("key", "mykey"); // Get your own key: http://api.imgur.com/

   // Create the XHR (Cross-Domain XHR FTW!!!)
   var xhr = new XMLHttpRequest();
   xhr.open("POST", "http://api.imgur.com/2/upload.json"); // Boooom!
   xhr.onload = function() {
      // Big win!
      // The URL of the image is:
      JSON.parse(xhr.responseText).upload.links.imgur_page;
   }

   // Ok, I don't handle the errors. An exercice for the reader.
   // And now, we send the formdata
   xhr.send(fd);
}
</script>
</head>   

<body>

<button type="button" onclick="upload('test.png')">upload to imgur</button> 

</body>
</html>

The png file test.png is stored in the same directory as my html file.

score 3 · Answer 1 · answered Feb 12 '12 at 14:49

The file has to be a File object created with the HTML5 fileAPI, you can't just give it a file name and expect it to work.

Javascript has no access to the filesystem, it can only access files that are given to it using either drag and drop or a file input.

score 2 · Accepted Answer · edited May 23 '17 at 12:28

2

The example you are using expects that you use input element (type=file) to upload some image. Try this example. You can access image data using a Canvas like this.

To summarize, you'll need to do this:

Create new Image with your file (needs to be on local domain)
Draw the image to a Canvas at onload
Extract image data using this method
Pass that data to imgur like here

edited May 23 '17 at 12:28

Community

1
1

answered Feb 12 '12 at 14:54

Juho Vepsäläinen

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Thanks for the suggestions. For adding an image to the canvas, is that the image `id`? I assume I can't refer to it using the filename, based on @skimberk1's comment. – djq Feb 12 '12 at 15:53
There's no way to refer to the image using filename. You'll need to load it to an img element and then load its contents to a canvas using drawImage. It is important to do this latter part at the img's onload handler. Otherwise it won't work. – Juho Vepsäläinen Feb 12 '12 at 16:09
Thanks bebraw, that helps me understand the flow. I'm experimenting with http://html2canvas.hertzen.com/ at the moment; it looks like it will do part of these steps. – djq Feb 12 '12 at 16:34

Uploading a png to imgur using javascript

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