# Terser — JavaScript Minifier and Compressor for ES6+

> Terser is a JavaScript mangler and compressor toolkit for ES6+ code, forked from UglifyJS with full support for modern syntax including arrow functions, classes, template literals, and modules.

## Install

Save as a script file and run:

# Terser — JavaScript Minifier and Compressor for ES6+

## Quick Use
```bash
npm install terser
echo "const greet = (name) => { console.log(`Hello, ${name}!`); };" | npx terser --compress --mangle
# Output: const greet=e=>{console.log(`Hello, ${e}!`)};
```

## Introduction
Terser picks up where UglifyJS left off, providing a JavaScript parser, mangler, and compressor that fully supports ES2015+ syntax. It is the default minifier used by Webpack 5, Vite, Rollup, and most modern JavaScript build tools.

## What Terser Does
- Parses ES6+ JavaScript into an AST for analysis and transformation
- Compresses code by removing dead branches, inlining constants, and simplifying expressions
- Mangles variable and function names to short identifiers for smaller output
- Generates source maps to maintain debuggability after minification
- Supports top-level and per-function configuration for compress and mangle passes

## Architecture Overview
Terser processes JavaScript in three phases: parsing (source to AST using its own parser), compressing (AST-to-AST transformations that reduce code size), and output (AST to minified string with optional source map). The compressor applies multiple passes, each running a set of optimization rules like dead code elimination, constant folding, and function inlining. The mangler then renames local variables to short names, respecting scopes and reserved words.

## Self-Hosting & Configuration
- Install via npm: `npm install terser` (library) or `npm install -g terser` (CLI)
- Use the CLI: `terser input.js --compress --mangle -o output.min.js`
- Use the API: `const { minify } = require('terser'); await minify(code, options)`
- Configure compress options: `{ dead_code: true, drop_console: true, passes: 2 }`
- Generate source maps: `--source-map "url=output.min.js.map"`

## Key Features
- Full ES2015+ support including async/await, optional chaining, and nullish coalescing
- Multi-pass compression finds additional optimization opportunities on each pass
- Tree-shaking-friendly output preserves module structure for downstream bundlers
- Property mangling with `--mangle-props` for aggressive size reduction
- Configurable per-function annotations like `/*@__PURE__*/` for side-effect-free marking

## Comparison with Similar Tools
- **esbuild** — much faster but with fewer compression optimizations; Terser produces smaller output
- **SWC minifier** — Rust-based and faster; Terser has more mature compression heuristics
- **UglifyJS** — Terser's predecessor, limited to ES5 syntax only
- **Google Closure Compiler** — more aggressive optimizations but requires type annotations for best results

## FAQ
**Q: Why use Terser instead of esbuild for minification?**
A: Terser typically produces 5-15% smaller bundles due to its multi-pass compressor and advanced dead code elimination, at the cost of slower build times.

**Q: Does Terser handle TypeScript?**
A: No. Terser works on JavaScript output. Run TypeScript through `tsc` or a transpiler first, then minify the JavaScript with Terser.

**Q: Can I keep certain variable names from being mangled?**
A: Yes. Use `mangle: { reserved: ['myVar', 'jQuery'] }` to protect specific names.

**Q: Is Terser used by Webpack?**
A: Yes. Webpack 5 uses `terser-webpack-plugin` as its default JavaScript minimizer.

## Sources
- https://github.com/terser/terser
- https://terser.org/


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Source: https://tokrepo.com/en/workflows/asset-f4f16bb4
Author: Script Depot