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Simple utility for walking an ESTree-compliant AST, such as one generated by acorn.


npm i estree-walker


var walk = require('estree-walker').walk;
var acorn = require('acorn');

ast = acorn.parse(sourceCode, options); //

walk(ast, {
  enter(node, parent, prop, index) {
    // some code happens
  leave(node, parent, prop, index) {
    // some code happens

Inside the enter function, calling this.skip() will prevent the node's children being walked, or the leave function (which is optional) being called.

Call this.replace(new_node) in either enter or leave to replace the current node with a new one.

Call this.remove() in either enter or leave to remove the current node.

Why not use estraverse?

The ESTree spec is evolving to accommodate ES6/7. I've had a couple of experiences where estraverse was unable to handle an AST generated by recent versions of acorn, because it hard-codes visitor keys.

estree-walker, by contrast, simply enumerates a node's properties to find child nodes (and child lists of nodes), and is therefore resistant to spec changes. It's also much smaller. (The performance, if you're wondering, is basically identical.)

None of which should be taken as criticism of estraverse, which has more features and has been battle-tested in many more situations, and for which I'm very grateful.