3-0-traverser.js

function traverser(ast, visitor) {
  function traverseNode(node, parent) {
    let methods = visitor[node.type];

    if (methods && methods.enter) {
      methods.enter(node, parent);
    }
    switch (node.type) {
      case 'Program':
        traverseArray(node.body, node);
        break;
      case 'CallExpression':
        traverseArray(node.params, node);
        break;
      case 'NumberLiteral':
      case 'StringLiteral':
        break;
      default:
        throw new TypeError(node.type);
    }

    if (methods && methods.exit) {
      methods.exit(node.parent);
    }
  }

  function traverseArray(array, parent) {
    array.forEach(child => {
      traverseNode(child, parent);
    });
  }

  traverseNode(ast, null);
}

module.exports = traverser;