JS Minifier

Terser removes comments and whitespace, drops unreachable code and unused local variables, and rewrites expressions into shorter equivalents, such as turning simple if statements into && or ternaries. With Mangle names on, local variables, parameters and local functions get one- or two-letter names. The values of strings, template literals and regular expressions never change, though quotes and escape sequences may be rewritten.

Yes for typical code: Terser parses the source and only applies transforms that keep its behavior, so URLs inside strings, regex literals and code without semicolons are handled correctly. Code that depends on function or class names at runtime, such as fn.name or constructor.name checks, can break when names are shortened, so turn off Mangle names for it.

If the code has top-level import or export statements, or uses top-level await, it is minified as a strict-mode module: imports and exported names are kept, while other top-level names are shortened or removed when unused. Plain scripts keep their top-level names, since other scripts or inline handlers may use them as globals.

Not fully. A formatter such as Prettier restores indentation and line breaks, but comments are gone and shortened names can't be recovered. This tool doesn't generate source maps, so use Terser, esbuild or your bundler's production build when you need them.