@jsquash/jpeg

An easy experience for encoding and decoding JPEG images in the browser. Powered by WebAssembly ⚡️.

Uses the MozJPEG library.

A jSquash package. Codecs and supporting code derived from the Squoosh app.

Installation

npm install --save @jsquash/jpeg
# Or your favourite package manager alternative

Usage

Note: You will need to either manually include the wasm files from the codec directory or use a bundler like WebPack or Rollup to include them in your app/server.

decode(data: ArrayBuffer): Promise

Decodes JPEG binary ArrayBuffer to raw RGB image data.

data

Type: ArrayBuffer

Example

import { decode } from '@jsquash/jpeg';

const formEl = document.querySelector('form');
const formData = new FormData(formEl);
// Assuming user selected an input jpeg file
const imageData = await decode(await formData.get('image').arrayBuffer());

encode(data: ImageData, options?: EncodeOptions): Promise

Encodes raw RGB image data to JPEG format and resolves to an ArrayBuffer of binary data.

data

Type: ImageData

options

Type: Partial<EncodeOptions>

The MozJPEG encoder options for the output image. See default values.

Example

import { encode } from '@jsquash/jpeg';

async function loadImage(src) {
  const img = document.createElement('img');
  img.src = src;
  await new Promise(resolve => img.onload = resolve);
  const canvas = document.createElement('canvas');
  [canvas.width, canvas.height] = [img.width, img.height];
  const ctx = canvas.getContext('2d');
  ctx.drawImage(img, 0, 0);
  return ctx.getImageData(0, 0, img.width, img.height);
}

const rawImageData = await loadImage('/example.png');
const jpegBuffer = await encode(rawImageData);

Manual WASM initialisation (not recommended)

In most situations there is no need to manually initialise the provided WebAssembly modules. The generated glue code takes care of this and supports most web bundlers.

One exception is CloudFlare workers. The environment at this time (this could change in the future) does not allow code to be dynamically imported. It needs to be bundled at runtime. WASM modules are set as global variables. See the Cloudflare workers example.

The encode and decode modules both export an init function that can be used to manually load the wasm module.

import decode, { init as initJpegDecode } from '@jsquash/jpeg/decode';

const WASM_MODULE = // A WebAssembly.Module object of the compiled wasm binary
initJpegDecode(WASM_MODULE);
const image = await fetch('./image.jpeg').then(res => res.arrayBuffer()).then(decode);