Parsing Javascript code and extracting variables and functions

9 points · submitted Apr 2016 by u/Denvildaste · help

I have some Javascript files, I want to write a tool to extract variables, functions and any other meaningful details.

For example file1.js:

var x = 1;
var y = 2;

function sum(a, b) {
   var result = a+b;
   return result;
}

So once I analyze this file I would get something similar to:

"vars": [{"name": "x", "value": 1}, {"name": "y", "value": 2}]
"functions": [{"name": "sum", "parameters": ["a", "b"], "vars": [...], "functions": [...]}]

It would be really great if I could narrow the results to scope, so for example "var result" is declared inside sum, I would love to learn about it.

Basically what I'm aiming for is to get as much information as possible from those files and then run some analysis to detect redundancies, etc...

What would be the best way to do this? Should I just write regex to parse those files or are there any decent libraries that would make this easy for me? It doesn't matter which language those libraries are in.

5 comments · 91% upvoted · other discussions

comments

ninth_reddit_account 7 points · Apr 2016

You want to generate an AST and crawl through that to get what you need. See this site for a demo of how that would work http://astexplorer.net/ which uses acorn https://github.com/ternjs/acorn

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fforw 2 points · Apr 2016

If you want to have information about scoping etc, the already mentioned acornjs is not going to be enough, since it just provides the static AST tree, I think. Babel plugins receive information about scoping and the ability to introduce new vars etc.

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bidi82 1 points · Apr 2016

Another option would be to use https://github.com/jquery/esprima to perform the parsing and AST building for you.

I'm not familiar with the AST it produces but even if it does not include scoping information, you can extract it yourself from the AST or maybe even find a project that does it for you as its AST's structure is a standard. https://github.com/estree/estree

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