UglifyJS 3 is a JavaScript parser, minifier, compressor, and beautifier toolkit designed for processing JavaScript code. The tool supports JavaScript and most ECMAScript language features, though exotic ECMAScript features may require preprocessing with transpilers like Babel before using UglifyJS. Key capabilities include: - JavaScript parsing and syntax analysis - Code minification to reduce file size - Code compression for optimization - Code beautification for improved readability - Command-line interface for batch processing - Programmatic API for integration into development workflows UglifyJS 3 features a simplified API and CLI that is not backwards compatible with version 2. The tool can process multiple input files simultaneously, parsing them in sequence within the same global scope to maintain proper variable and function references across files. Installation options include global installation via NPM for command-line usage or local installation for programmatic integration. The tool accepts input from files or STDIN and provides flexible command-line options for various processing scenarios.