Execute a callback on every node of a source code's AST and stop walking when you see fit

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4115.0.0a year ago9 years agoMinified + gzip package size for node-source-walk in KB


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

npm install node-source-walk


const Walker = require('node-source-walk');

const 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, (node) => {
  if (node.type === whateverImLookingFor) {
    // No need to keep traversing since we found what we wanted

By default, Walker will use @babel/parser (supporting ES6, JSX, Flow, and all other available @babel/parser plugins) and the sourceType: module, but you can change any of the defaults as follows:
const walker = new Walker({
  sourceType: 'script',
  // If you don't like experimental plugins
  plugins: [

  • The supplied options are passed through to the parser, so you can configure it according to @babel/parser's documentation.

Swap out the parser

If you want to supply your own parser, you can do:
const 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 @babel/parser by default).