_____ _      _____ __  __ _____ _______ ____  _  __
 / ____| |    |_   _|  \/  |_   _|__   __|___ \| |/ /
| (___ | |      | | | \  / | | |    | |    __) | ' /
 \___ \| |      | | | |\/| | | |    | |   |__ <|  <
 ____) | |____ _| |_| |  | |_| |_   | |   ___) | . \
|_____/|______|_____|_|  |_|_____|  |_|  |____/|_|\_\

Welcome to SlimIt3k

SlimIt3k is a Python 3-only fork of SlimIt, a JavaScript minifier written in Python. This fork was created because the original SlimIt was not updated on PyPI and no longer works with modern Python versions due to use of use_2to3, which was removed in setuptools 58.0.0.

SlimIt3k compiles JavaScript into more compact code so that it downloads and runs faster.

SlimIt3k also provides a library that includes a JavaScript parser, lexer, pretty printer and a tree visitor.

Current maintainer: Antti Haapala <[email protected]>

https://slimit.readthedocs.io/

Installation

$ pip install slimit3k

Or the bleeding edge version from the git master branch:

$ pip install git+https://github.com/tetframework/slimit3k.git#egg=slimit3k

Let's minify some code

From the command line:

$ slimit -h
Usage: slimit [options] [input file]

If no input file is provided STDIN is used by default.
Minified JavaScript code is printed to STDOUT.

Options:
  -h, --help            show this help message and exit
  -m, --mangle          mangle names
  -t, --mangle-toplevel
                        mangle top level scope (defaults to False)

$ cat test.js
var foo = function( obj ) {
        for ( var name in obj ) {
                return false;
        }
        return true;
};
$
$ slimit --mangle < test.js
var foo=function(a){for(var b in a)return false;return true;};

Or using library API:

>>> from slimit import minify
>>> text = """
... var foo = function( obj ) {
...         for ( var name in obj ) {
...                 return false;
...         }
...         return true;
... };
... """
>>> print(minify(text, mangle=True, mangle_toplevel=True))
var a=function(a){for(var b in a)return false;return true;};

Iterate over, modify a JavaScript AST and pretty print it

>>> from slimit.parser import Parser
>>> from slimit.visitors import nodevisitor
>>> from slimit import ast
>>>
>>> parser = Parser()
>>> tree = parser.parse('for(var i=0; i<10; i++) {var x=5+i;}')
>>> for node in nodevisitor.visit(tree):
...     if isinstance(node, ast.Identifier) and node.value == 'i':
...         node.value = 'hello'
...
>>> print(tree.to_ecma())  # print awesome javascript :)
for (var hello = 0; hello < 10; hello++) {
  var x = 5 + hello;
}
>>>

Writing custom node visitor

>>> from slimit.parser import Parser
>>> from slimit.visitors.nodevisitor import ASTVisitor
>>>
>>> text = """
... var x = {
...     "key1": "value1",
...     "key2": "value2"
... };
... """
>>>
>>> class MyVisitor(ASTVisitor):
...     def visit_Object(self, node):
...         """Visit object literal."""
...         for prop in node:
...             left, right = prop.left, prop.right
...             print(f"Property key={left.value}, value={right.value}")
...             # visit all children in turn
...             self.visit(prop)
...
>>>
>>> parser = Parser()
>>> tree = parser.parse(text)
>>> visitor = MyVisitor()
>>> visitor.visit(tree)
Property key="key1", value="value1"
Property key="key2", value="value2"

Using lexer in your project

>>> from slimit.lexer import Lexer
>>> lexer = Lexer()
>>> lexer.input('a = 1;')
>>> for token in lexer:
...     print token
...
LexToken(ID,'a',1,0)
LexToken(EQ,'=',1,2)
LexToken(NUMBER,'1',1,4)
LexToken(SEMI,';',1,5)

You can get one token at a time using token method:

>>> lexer.input('a = 1;')
>>> while True:
...     token = lexer.token()
...     if not token:
...         break
...     print token
...
LexToken(ID,'a',1,0)
LexToken(EQ,'=',1,2)
LexToken(NUMBER,'1',1,4)
LexToken(SEMI,';',1,5)

LexToken instance has different attributes:

>>> lexer.input('a = 1;')
>>> token = lexer.token()
>>> token.type, token.value, token.lineno, token.lexpos
('ID', 'a', 1, 0)

Benchmarks

SAM - JQuery size after minification in bytes (the smaller number the better)

Original jQuery 1.6.1 (bytes)	SlimIt SAM	rJSmin SAM	jsmin SAM
234,995	94,290	134,215	134,819

Roadmap

• when doing name mangling handle cases with 'eval' and 'with'
• foo["bar"] ==> foo.bar
• consecutive declarations: var a = 10; var b = 20; ==> var a=10,b=20;
• reduce simple constant expressions if the result takes less space: 1 +2 * 3 ==> 7
• IF statement optimizations
  1. if (foo) bar(); else baz(); ==> foo?bar():baz();
  2. if (!foo) bar(); else baz(); ==> foo?baz():bar();
  3. if (foo) bar(); ==> foo&&bar();
  4. if (!foo) bar(); ==> foo||bar();
  5. if (foo) return bar(); else return baz(); ==> return foo?bar():baz();
  6. if (foo) return bar(); else something(); ==> {if(foo)return bar();something()}
• remove unreachable code that follows a return, throw, break or continue statement, except function/variable declarations
• parsing speed improvements

Acknowledgments

• The lexer and parser are built with PLY
• Several test cases and regexes from jslex
• Some visitor ideas - pycparser
• Many grammar rules are taken from rkelly
• Name mangling and different optimization ideas - UglifyJS
• ASI implementation was inspired by pyjsparser

License

The MIT License (MIT)