mozjpeg.js is a port of MozJPEG to JavaScript, via Emscripten. MozJPEG is a JPEG encoder by Mozilla that creates smaller JPEGs at the expense of longer encoding times. It exposes MozJPEG’s cjpeg command functionality as a JavaScript function, and can be used from both within the browser and Node.js.


const mozjpeg = require("mozjpeg-js");
const fs = require("fs");

const input = fs.readFileSync("in.ppm");
const out = mozjpeg.encode(input, { quality: 85 });
// out = { data: <mozjpeg output>, stderr: <cjpeg stderr> }


mozjpeg.encode accepts a typed array of data and an object containing options to pass to cjpeg. It returns an object containing the output JPEG in data as a Uint8Array and a string containing stderr in stderr.