gavo.imp.rjsmin module

Javascript Minifier

rJSmin is a javascript minifier written in python.

The minifier is based on the semantics of jsmin.c by Douglas Crockford.


Copyright 2011 - 2019 André Malo or his licensors, as applicable


Licensed under the Apache License, Version 2.0 (the “License”); you may not use this file except in compliance with the License. You may obtain a copy of the License at

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an “AS IS” BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.

The module is a re-implementation aiming for speed, so it can be used at runtime (rather than during a preprocessing step). Usually it produces the same results as the original jsmin.c. It differs in the following ways:

  • there is no error detection: unterminated string, regex and comment literals are treated as regular javascript code and minified as such.

  • Control characters inside string and regex literals are left untouched; they are not converted to spaces (nor to n)

  • Newline characters are not allowed inside string and regex literals, except for line continuations in string literals (ECMA-5).

  • “return /regex/” is recognized correctly.

  • More characters are allowed before regexes.

  • Line terminators after regex literals are handled more sensibly

  • “+ +” and “- -” sequences are not collapsed to ‘++’ or ‘–’

  • Newlines before ! operators are removed more sensibly

  • (Unnested) template literals are supported (ECMA-6)

  • Comments starting with an exclamation mark (!) can be kept optionally

  • rJSmin does not handle streams, but only complete strings. (However, the module provides a “streamy” interface).

Since most parts of the logic are handled by the regex engine it’s way faster than the original python port of jsmin.c by Baruch Even. The speed factor varies between about 6 and 55 depending on input and python version (it gets faster the more compressed the input already is). Compared to the speed-refactored python port by Dave St.Germain the performance gain is less dramatic but still between 3 and 50 (for huge inputs). See the docs/BENCHMARKS file for details.

rjsmin.c is a reimplementation of in C and speeds it up even more.

Supported python versions are 2.7 and 3.4+.

gavo.imp.rjsmin.jsmin(script, keep_bang_comments=False)

Minify javascript based on jsmin.c by Douglas Crockford.

Instead of parsing the stream char by char, it uses a regular expression approach which minifies the whole script with one big substitution regex.


This is a hand crafted C implementation built on the regex semantics.


Script to minify


Keep comments starting with an exclamation mark? (/*!...*/)


Minified script