ParseJS is a JavaScript parser written in Ruby using the KPeg parser generator. It also takes a JavaScript parse tree and emits semantically identical JavaScript. The parser is tested by parsing large, popular JavaScript libraries (such as jQuery) and confirming that the minified output after a round-trip through ParseJS is the same as minifying the original source.
The ParseJS stringifier does not guarantee equivalent whitespace and comments in a round-trip, but it should guarantee semantic equivalence.
The ParseJS parser maintains comments in most cases where comments would represent inline documentation.
- top-level statement: a ParseJS top-level statement node contains any comment that immediately preceded it.
- property: in a property list (object literal), a property node contains any comment that immediately preceded it.
There is a work-in-progress AST walker that associates comments with particular structures. The ultimate goal of this walker is to identify JavaScript structures that represent "classes" or similar structures and associate their comments with information extracted from the code.
ParseJS is provided as a Rubygem. At the moment, you can use it in your Gemfile by using Bundler's git feature.
gem "parsejs", :git => "git://github.com/wycats/parsejs.git"You can parse a String of JavaScript and receive an AST by using
ParseJS.parse.
ast = ParseJS.parse(some_data)You can convert the AST back into a JavaScript String using the stringifier. You can mutate the AST before converting it into a String if you wish.
ParseJS::Stringifier.to_string(ast)
You can write your own AST walker without implementing visitors for all
nodes by subclassing ParseJS::Visitor. Take a look
at that class
to see the default visitor behavior for a particular node.
By default, nodes accept their children. Nodes that have children that
are Arrays of nodes (e.g. FunctionDeclaration, which has an Array of
parameters and an Array of statements as children) default to looping
over the Arrays and accepting their members.
You can take a look at the in-progress
docs extractor
or the stringifier
for examples of subclasses of ParseJS::Visitor.
Copyright (C) 2012 Yehuda Katz
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