Download and return image data for the first frame of an animated GIF.

Use when you want to display a static preview image of the first frame of an animated GIF on the frontend without downloading the entire GIF.

If you don't need to parse the whole GIF, this method is less complicated and faster than using a backend service like GraphicsMagick to download the full GIF and extract the first frame or using a frontend library like buzzfeed/libgif-js to download and parse the full GIF, pause on the first frame.

Works by downloading the GIF one part at a time, inspecting the bytes to look for an end of frame, and either stopping download and returning first frame data if reached, or continuing to download another chunk and repeat.

Forked from voxmedia/vax-fig to remove Ruby and jQuery depencencies and to turn into an npm package.

Install: npm install preview-gif

PreviewGIF is a function that takes two parameters:

1. URL of an animated GIF
2. Callback function of the form callback(err, imageData). err either null or an object with type and message properties. imageData, if there is no error, is a base64-encoded string of the first frame of image data that can be assigned directly to an image's src attribute to display it.

<img data-src="some.gif" id="some-gif" />
<!-- Important! Don't put the GIF url in the `src` attribute, or the browser
     will automatically download the full GIF which defeats the purpose of
     this tool -->

const PreviewGIF = require('preview-gif');

const gif = document.getElementById('some-gif');

PreviewGIF(gif.dataset.src, (err, imageData) => {
  if (err) console.error(err);
  else gif.src = imageData;
});

See demo/index.html.

• Probably will not work in old versions of IE.

• @jesse
• GIF decoder borrowed from @deanm's omggif plugin
• Base64 encoder borrowed from n1k0 via http://stackoverflow.com/a/7372816
• Core functionality extracted into an npm module that doesn't require jQuery by @liddiard

Copyright (c) 2014, Vox Media, Inc. with modifications by Harrison Liddiard. All rights reserved.

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