Compressor.js is a lightweight JavaScript library for in-browser image compression that allows developers to reduce file sizes before uploading images to a server, improving performance and user experience. It works by taking an input image (such as from a file input) and resizing or reencoding it on the client side according to developer-specified options like maximum width, height, quality, and MIME type. Because compression happens in the browser, users upload smaller images without sacrificing responsiveness or relying on server resources, which is especially useful for mobile users or limited-bandwidth environments. The library supports modern browsers and automatically handles orientation based on EXIF metadata, ensuring images appear correctly after compression.