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https://github.com/sindresorhus/is-progressive
Check if JPEG images are progressive
https://github.com/sindresorhus/is-progressive
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Check if JPEG images are progressive
- Host: GitHub
- URL: https://github.com/sindresorhus/is-progressive
- Owner: sindresorhus
- License: mit
- Created: 2015-01-10T14:04:25.000Z (almost 10 years ago)
- Default Branch: main
- Last Pushed: 2023-05-27T14:58:50.000Z (over 1 year ago)
- Last Synced: 2024-04-14T09:53:04.947Z (7 months ago)
- Language: JavaScript
- Homepage:
- Size: 117 KB
- Stars: 200
- Watchers: 12
- Forks: 7
- Open Issues: 0
-
Metadata Files:
- Readme: readme.md
- License: license
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README
# is-progressive
> Check if JPEG images are [progressive](http://www.faqs.org/faqs/jpeg-faq/part1/section-11.html)
Can be useful to make sure your images are progressive, which is important for performance:
> Progressive JPEGs are better because they are faster. Appearing faster is being faster, and perceived speed is more important that actual speed. - [Progressive JPEGs: a new best practice](https://calendar.perfplanet.com/2012/progressive-jpegs-a-new-best-practice/)
The check is fast as it only reads a small part of the file.
## Install
```sh
npm install is-progressive
```
## Usage
```js
import isProgressive from 'is-progressive';
console.log(await isProgressive.file('baseline.jpg'));
//=> false
isProgressive.fileSync('progressive.jpg');
//=> true
```
```js
// Check if a remote JPEG image is progressive without downloading the whole file
import https from 'node:https';
import isProgressive from 'is-progressive';
const url = 'https://raw.githubusercontent.com/sindresorhus/is-progressive/main/fixture/progressive.jpg';
https.get(url, async response => {
console.log(await isProgressive.stream(response));
//=> true
});
```
### API
Prefer the file methods if you're dealing directly with files. Those methods are optimized to read in the least amount of bytes necessary to determine whether it's a progressive JPEG image.
#### .buffer(buffer)
Returns whether the `buffer` is a progressive JPEG image.
##### buffer
Type: `Uint8Array`
The buffer of a JPEG image.
Must be at least `65535` bytes when the file is larger than that.
#### .stream(stream)
Returns a `Promise` indicating whether the file stream is a progressive JPEG image.
##### stream
Type: `stream.Readable`
A data stream with a JPEG image.
#### .file(filePath)
Returns a `Promise` indicating whether the file at the `filePath` is a progressive JPEG image.
##### filePath
Type: `string`
The file path to the image.
#### .fileSync(filePath)
Whether the file at the `filePath` is a progressive JPEG.
##### filePath
Type: `string`
The file path to the image.
## Build-system integration
Don't use this with a build-system like Gulp/Grunt as you can easily make the images progressive with the [`imagemin`](https://github.com/imagemin/imagemin) *([Gulp](https://github.com/sindresorhus/gulp-imagemin)/[Grunt](https://github.com/gruntjs/grunt-contrib-imagemin)-task)* `progressive` option instead of just warning about it.
## Related
- [is-progressive-cli](https://github.com/sindresorhus/is-progressive-cli) - CLI for this module