code: function optimizePropertyAccess(node) {
    var ok =
      node.type === "MemberExpression" &&
      node.computed &&
      node.property.type === "Literal" &&
      typeof node.property.value === "string" &&
      isSafe(node.property.value);
    if (ok) {
      var id = es.Identifier(null, node.property.value);
      return es.MemberExpression(null, false, node.object, id);
    }
  }
docs: Turns `foo["bar"]` into `foo.bar`