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

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

https://slimit.readthedocs.io/

$ [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 athttp://packages.debian.org/sid/slimit

From the command line:

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

Or using library API:

>>>from slimitimport minify>>> text="""... var foo= function( obj ) {...for ( var namein 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;};

>>>from slimit.parserimport Parser>>>from slimit.visitorsimport nodevisitor>>>from slimitimport ast>>>>>> parser= Parser()>>> tree= parser.parse('for(var i=0; i<10; i++) {var x=5+i;}')>>>for nodein nodevisitor.visit(tree):...ifisinstance(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;}>>>

>>>from slimit.parserimport Parser>>>from slimit.visitors.nodevisitorimport ASTVisitor>>>>>> text="""... var x= {..."key1":"value1",..."key2":"value2"... };...""">>>>>>classMyVisitor(ASTVisitor):...defvisit_Object(self,node):..."""Visit object literal."""...for propin 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"

>>>from slimit.lexerimport Lexer>>> lexer= Lexer()>>> lexer.input('a = 1;')>>>for tokenin 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 usingtoken method:

>>> lexer.input('a = 1;')>>>whileTrue:...     token= lexer.token()...ifnot 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)

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

• 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 orcontinue statement, except function/variable declarations
• parsing speed improvements

• The lexer and parser are built withPLY
• Several test cases and regexes fromjslex
• Some visitor ideas -pycparser
• Many grammar rules are taken fromrkelly
• Name mangling and different optimization ideas -UglifyJS
• ASI implementation was inspired bypyjsparser

The MIT License (MIT)