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

Welcome to SlimIt

SlimIt is a JavaScript minifier written in Python. It compiles JavaScript into more compact code so that it downloads and runs faster.

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

https://slimit.readthedocs.io/ <https://slimit.readthedocs.io/>_

Installation

$ [sudo] pip install slimit

Or the bleeding edge version from the git master branch:

$ [sudo] pip install git+https://github.com/rspivak/slimit.git#egg=slimit

There is also an official DEB package available at http://packages.debian.org/sid/slimit <http://packages.debian.org/sid/slimit>_

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 'Property key=%s, value=%s' % (left.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 <http://www.dabeaz.com/ply/>_
Several test cases and regexes from jslex <https://bitbucket.org/ned/jslex>_
Some visitor ideas - pycparser <http://code.google.com/p/pycparser/>_
Many grammar rules are taken from rkelly <https://github.com/tenderlove/rkelly>_
Name mangling and different optimization ideas - UglifyJS <https://github.com/mishoo/UglifyJS>_
ASI implementation was inspired by pyjsparser <http://bitbucket.org/mvantellingen/pyjsparser>_

License

The MIT License (MIT)

rspivak / slimit

readme