Can we use the ES6 class syntax in AWS Lambda?

Question

I would like to use the ES6 class syntax in AWS Lambda using Node 6.10, but I cannot get it to work:

class widget {
    constructor(event, context, callback) {
        callback(null, `all seems well!`);
    }
}

// module.exports.handler = widget; // "Process exited before completing request"
module.exports.handler = new widget(); // "callback is not a function"

Has anyone had success with using the class syntax? The class constructor does not get seen as a handler function apparently.

Answer 1

You are not following the API that Lambda expects. As the documentation says, it expects

exports.myHandler = function(event, context, callback) {};

which it would then call with

const handlers = require('your-module');
handlers();

The issue here is that ES6 classes need to be created with new. Since the Lambda API says it expects a function, it expects a callable function, not a constructable function. If you want to use a class, you'd need to export a function, e.g.

class widget {
  constructor(event, context, callback) {
    callback(null, `all seems well!`);
  }
}

exports.myHandler = function(event, context, callback) {
    new widget(event, context, callback);
};

Answer 2

To answer to your question, yes, you can use ES6 classes with the Node 6 Lambda functions. But this code is not going to work.

The lambda handler is not going to call new on your class so your constructor won't fire if you just pass

module.exports.handler = widget;

It will call widget(event, context, callback). If you call new before you pass it it off, then you don't yet have the callback reference from the handler. You are essentially creating a new object with no initialized values. You're calling new widget() but you're not passing anything it and then you are passing this new instance for the handler to call.

There's no reason on earth (as far as I can tell) to do this, but you could:

class widget extends Function {
    constructor(){
      super('...args', 'return this.__call__(...args)');
      return this.bind(this);    
    }

    __call__(event, context, callback) {
     callback(null, "Dude, this is wierd.")
   }
}
exports.handler = new widget()