babel-q

babel-q

babel-q offers a way to query an babel AST to find specific patterns using a syntax somewhat similar to XPath. babel-q was inspired by astq, but offers some features that did not seem possible in astq and also has some limits compared to astq.

Goals:

• Should try to traverse the AST only once when resolving the Query
• Should allow filtering of nodes
• Allow running multiple queries at the same time without traversing the AST multiple times

Example

The following pattern:

//AssignmentExpression[
      /MemberExpression[
        /:property/:name == "migrateVersion" && 
        /$:object == ../../../../:params
      ]
    ]/:right/:value

tries to find the following code snippet and returns the string value assigned to the migrateVersion property:

...
  function( jQuery, window ) {
    ...
    jQuery.migrateVersion = "3.4.1";
    ...
  }
...

Find an AssignmentExpression at arbitrary depth, which directly contains a MemberExpression where the property name is "migrateVersion" and the object is bound to a parameter of the surrounding function, an return the assigned value.

Grammar

• /<node type> - find a child node of the given type
• //<node type> - find a descendant of the given type
• /:<name> - find an attribute of the current node with the given name
• //:<name> - find an attribute of the current node with the given name regardless of whether it's on the current node or on a descendant
• /$:<name> - find the binding of an Identifier
• /$$:<name> - return the binding or the attribute if binding cannot be resolved (helpful if a variable is sometimes directly assigned and sometimes not)
• [] - apply a filter to the node
• &&, || - logical conditions of a filter
• == - comparison in filter
• ../ - go to parent in filter (use with care, as this causes extra traversal)
• /* - wildcard type child
• //* - wildcard type descendant
• '<some value>',"<some value>" - a string literal
• /fn:first(selector) - returns the first result from all matches
• /fn:concat(...selectors...) - concatenates results. If an argument has more than one value, those will be concatenated first.
• /fn:join(selector, ",") - concatenates the results of a selector with the given separator

API

• query(code: ParseResult<Babel.File> | string, query: string) : Result[] - Runs the given query on the given code in the form of an already parsed AST or a string (which is parsed as sourceType: "unambiguous"), and returns the result.
• multiQuery<T extends Record<string, string>>(code: ParseResult<Babel.File> | string, namedQueries: T) : Record<keyof T, Result[]> - Runs the given set of named queries on the given code in the form of an already parsed AST or a string (which is parsed as sourceType: "unambiguous"), and returns a map of named results (one result array per named query).

where Result is Babel.Node | string | number | boolean;

Example code

import { query } from "babel-q";
import * as fs from "fs";

const contents = fs.readFileSync("some-file.js");

const result = query(
  contents,
  `//FunctionDeclaration/:id/:name`
);

console.log("Function names", result);