fetch base64 string failed on Safari

[LXVC]

here is my code, work well on Chrome56:

function dataURItoFile(dataURI, filename) {
  const mimeType = dataURI.split(',')[0].split(':')[1].split(';')[0]
  return fetch(dataURI)
    .then(res => res.arrayBuffer())
    .then(buf => new File([buf], filename, { type: mimeType }))
}

dataURI: base64 string

but on Safari10:

XMLHttpRequest cannot load data:image/png;base64,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....

so, is that a bug?

[jimmywarting]

The problem

It boils down to this code:

url = "data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAUAAAAFCAYAAACNbyblAAAAHElEQVQI12P4//8/w38GIAXDIBKE0DHxgljNBAAO9TXL0Y4OHwAAAABJRU5ErkJggg=="
xhr = new XMLHttpRequest
xhr.open('GET', url)
xhr.send()

When sortering the url i saw the full error message:

XMLHttpRequest cannot load < URL >. Cross origin requests are only supported for HTTP.

I tested the same code in Safari TP and it worked just fine. So did the native fetch version of your code also.

Workaround

Use any other way to make a File out of a base64. Make your pick: http://stackoverflow.com/questions/16245767/creating-a-blob-from-a-base64-string-in-javascript

Code review

using blob instead of arraybuffer yields a better result, you don't have to get the mimeType from the base64 since it will be included when you return the blob. Beside blob may also be a better choice for you since you can't construct files on all browsers (see note 2 on caniuse.com)

  return fetch(dataURI)
    .then(res => res.blob())
    .then(blob => new File([blob], filename, { type: blob.type }))

What can the polyfill do to fix it?

Parse the url, see if it's a data URI and if it's convert the data URI to a blob internally without using xhr

[LXVC]

Thank you!

[mislav]

@jimmywarting Thanks for your extensive research. Do you think this is something we should aim to fix in our polyfill? If not, I'm keen on closing this out.

[jimmywarting]

I'm on the fence.
It would be nice if it worked but I also thing its a bad practise to have a base64 URL to begin with.
Think you should always aim to have a arrays buffers or blob. Decoding and encoding is only a unnecessary overhead and there are better ways to handle it IMAO

[mislav]

I would agree on a workaround if it was easy (e.g. 2–3 lines of code). However, since the logic to convert a base64 would inflate the size of this polyfill, I don't think this is something that we should be working around of, and instead it should be the responsibility of the user to avoid using fetch() for this on unsupporting browsers.