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node-source-walk npm npm

Synchronously execute a callback on every node of a file's AST and stop walking whenever you see fit.

npm install --save node-source-walk


  var Walker = require('node-source-walk');
  var walker = new Walker();
  // Assume src is the string contents of myfile.js
  // or the AST of an outside parse of myfile.js
  walker.walk(src, function(node) {
    if (node.type === whateverImLookingFor) {
      // No need to keep traversing since we found what we wanted

By default, Walker will use babylon (supporting ES6, JSX, Flow, and all other available babylon plugins) and the sourceType: module, but you can change any of the defaults as follows:

var walker = new Walker({
  sourceType: 'script',
  // If you don't like experimental plugins
  plugins: [

Swap out the parser

If you want to supply your own parser, you can do:

var walker = new Walker({
  parser: mySweetParser
  • The custom parser must have a .parse method that takes in a string and returns an object/AST.
  • All of the other options supplied to the Walker constructor will be passed along as parser options to your chosen parser.

Public Members

walk(src, cb)

  • Recursively walks the given src from top to bottom
  • src: the contents of a file OR its (already parsed) AST
  • cb: a function that is called for every visited node.
  • The argument passed to cb will be the currently visited node.

moonwalk(node, cb)

  • Recursively walks up an AST starting from the given node. This is a traversal that's in the opposite direction of walk and traverse.
  • node: a valid AST node
  • cb: a function that is called for every node (specifically via visiting the parent(s) of every node recursively).
  • The argument passed to cb will be the currently visited node.


  • Halts further walking of the AST until another manual call of walk or moonwalk.
  • This is super-beneficial when dealing with large source files (or ASTs)

traverse(node, cb)

  • Allows you to traverse an AST node and execute a callback on it
  • Callback should expect the first argument to be an AST node, similar to walk's callback.


  • Uses the options supplied to Walker to parse the given source code string and return its AST using the configured parser (or babylon by default).