CODEWITHSUNDEEP
javascriptbabeljs
Sophistifunk
Sophistifunk

Reputation: 5042

How do I get Babel to output a file's AST?

Is there a way I can get Babel to output the AST of a file, as a JSON or similar, rather than condense it back into JS?

The reason is that I want to be able to do some simple static analysis / code gen, and while I aim to eventually do it within a plugin for Babel (or similar), I feel it would simplify things significantly if I can start with a static model.

Upvotes: 3

Views: 4451

Answers (2)

Rūdolfs Vikmanis
Rūdolfs Vikmanis

Reputation: 722

There's babylon, babel's own parser:

npm install -g babylon

babylon your_file.js > ast.json

Node API example and source: https://github.com/babel/babel/tree/master/packages/babylon

Also the babel plugin handbook might come in handy for AST reference, and to get started with plugin development.

Upvotes: 9

Leah Zorychta
Leah Zorychta

Reputation: 13429

you should check out ast-source - it can take babel as a parser when it builds the tree.

Example from their npmjs page:

import ASTSource from "ast-source"
import estraverse from "estraverse"
import fs from "fs"

function transform(AST) {
    var replaced = {
        "type": "babel",
        "value": 42,
        "raw": "42"
    };
    return estraverse.replace(AST, {
        enter: function (node) {
            if (node.type === estraverse.Syntax.Literal) {
                return replaced;
            }
        }
    });
}

var source = new ASTSource(fs.readFileSync("./input.js", "utf-8"), {
    filePath: "./input.js"
});
var output = source.transform(transform).output();
console.log(output.code);// => "var a = 42;" 
console.dir(output.map.toString()); // => source map 
fs.writeFileSync("./output.js", output.codeWithMap, "utf-8");

Upvotes: 3

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