function tenTimes (cb) {
  for (var i = 0; i < 10; i += 1) {
    cb();
  }
}

const visitor1 = {
  enter: function (currentNode, parentNode) {
    switch(currentNode.type) {
    case 'ForStatement':
      console.log('v1: going to skip ' + currentNode.type);
      this.skip();
      break;
    case 'CallExpression':
    case 'FunctionDeclaration':
      console.log('v1: entering ' + currentNode.type);
      break;
    }
    return undefined;
  },
  leave: function (currentNode, parentNode) {
    switch(currentNode.type) {
    case 'ForStatement':
    case 'CallExpression':
    case 'FunctionDeclaration':
      console.log('v1: leaving ' + currentNode.type);
      break;
    }
  }
};

const visitor2 = {
  enter: function (currentNode, parentNode) {
    switch(currentNode.type) {
    case 'ForStatement':
    case 'CallExpression':
    case 'FunctionDeclaration':
      console.log('v2: entering ' + currentNode.type);
      break;
    }
  },
  leave: function (currentNode, parentNode) {
    switch(currentNode.type) {
    case 'ForStatement':
    case 'CallExpression':
    case 'FunctionDeclaration':
      console.log('v2: leaving ' + currentNode.type);
      break;
    }
  }
};

const mergeVisitors = require('merge-estraverse-visitors');
const estraverse = require('estraverse');
const { parse } = require('acorn');
const ast = parse(code);
const mergedVisitor = mergeVisitors([ visitor1, visitor2 ])
estraverse.traverse(ast, mergedVisitor);