The default function template for AWS Lambda in Zapier. Just create a Lambda function with this code named "zapier_eval" and we'll take care of the rest! This code is released to the public domain - feel free to customize, fork or repackage this.

default-lambda-eval.js

'use strict';

var domain = require('domain');

var userMethod = 'handler';
var userCodeWrapper = function(userCode) {
  return '\
"use strict";\n\
' +  userCode + '\n\
try {\n\
  if (' + userMethod + '.length > 1) {\n\
    ' + userMethod + '(userInput, callback);\n\
  } else {\n\
    callback(null, ' + userMethod + '(userInput));\n\
  }\n\
} catch(err) {\n\
  callback(err, null);\n\
}';
};

module.exports.handler = function(event, context) {
  var callback = function(err, val) {
    context.done(err, val);
  };

  var userCode = userCodeWrapper(event.userCode);

  var d = domain.create();
  d.on('error', function(err) {
    context.done(err, null);
  });
  d.run(function(){
    var wrapperFunc = new Function('require', 'userInput', 'callback', userCode);
    wrapperFunc(require, event.userInput, callback);
  });
};