slimit 0.5.5

SlimIt - JavaScript minifier

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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.

http://slimit.org/

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

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

Or using library API:

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

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)

Installation

Using pip:

$ [sudo] pip install slimit

Using easy_install:

$ [sudo] easy_install slimit

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

Change History

0.5.5 (2011-10-05)

• Bugfix: https://github.com/rspivak/slimit/issues/7

0.5.4 (2011-10-01)

• Bugfix: https://github.com/rspivak/slimit/issues/6 Division with “this” fails

0.5.3 (2011-06-29)

• Bugfix: https://github.com/rspivak/slimit/issues/5

0.5.2 (2011-06-14)

• Bugfix: https://github.com/rspivak/slimit/issues/4

• Bugfix: https://github.com/rspivak/slimit/issues/3

0.5.1 (2011-06-06)

• Bugfix: https://github.com/rspivak/slimit/issues/2

0.5 (2011-06-06)

• Added name mangling

0.4 (2011-05-12)

• Minify more by removing block braces { }

• More tests

0.3.2 (2011-05-09)

• More hacks to use pre-generated lex and yacc tables when called from the command line

0.3.1 (2011-05-09)

• Use pre-generated lex and yacc tables when called from the command line

0.3 (2011-05-09)

• Added minifier

0.2 (2011-05-07)

• Added a JavaScript parser

• Added pretty printer

• Added node visitor

0.1 (2011-05-02)

• Initial public version. It contains only a JavaScript lexer