How to send a function as payload of socket notification?

[ngnijland]

Hello,

When I receive a socket notification in my node_helper.js file I want to sent a socket notification with an object containing a function as value of one of its keys. Like this:

const NodeHelper = require('node_helper');
const someFunction = require('./someFunction');

module.exports = NodeHelper.create({
  start: function () {
    console.log('Start node helper');
  },

  socketNotificationReceived: function (notification) {
    if (notification === 'FOO') {
      this.sendSocketNotification('FOO', { bar: someFunction });
    }
  },
});

However, when I receive this notification inside my main module file the function is not present in the payload:

  socketNotificationReceived: function (notification, payload) {
    if (notification === 'FOO') {
      console.log(payload.bar); // This logs 'undefined'
    }
  },

Any other values (object, arrays, etc) I pass in the payload are received correctly.

Does somebody know why the function I pass with the payload is undefined when I receive the socket notification in my main module file?

[sdetweil]

@ngnijland I think u have to send the entire function in the packet. It can’t contain the address of anything on the other side

[ngnijland]

@sdetweil thanks for your reply!

I don’t think I completely understand you. What do you mean with “send the entire function”? Do you mean I can’t import a reference? And should write out the function in the node_helper.js file?

[A Former User]

@ngnijland
Impossible in the current MM legacy structure.
those processes are separated and can not share function.

2 reasons;

• The function itself cannot be transferred through socket (JSON doesn’t allow it)
• If the function depends on some dependencies, it will lose them.

Anyway, if the function itself is somehow simple and has no dependency, there could be some trick.

var originalPayload = {
  "something": "hello, world",
  "someFunc" : (value) => {
    console.log(value)
    return value
  }
}

originalPayload.someFunc("Original Execution.")


let replacer = (key, value) => {
  if (typeof value == "function") {
    return "__FUNC__" + value.toString()
  }
  return value
}

// Encode function in payload object
var encodedPayload = JSON.stringify(originalPayload, replacer, 2)
console.log("----")
console.log(encodedPayload)
console.log("----")
// encodedPayload will have;
// {
//   "something": "hello, world",
//   "someFunc": "__FUNC__(value) => {\n console.log(value)\n return value\n  }"
// }

// Now you can transfer this string as payload of socketNotification.
// this.sendSocketNotification("SOME_EVENT", encodedPayload)
// ...

// Let's assume you got a payload through socketNotification
var receivedPayload = encodedPayload

let reviver = (key, value) => {
  if (typeof value === 'string' && value.indexOf('__FUNC__') === 0) {
    value = value.slice(8)
    let functionTemplate = `(${value})`
    return eval(functionTemplate)
  }
  return value
}

var revivedPayload = JSON.parse(receivedPayload, reviver)
revivedPayload.someFunc("Function is revived.")

CAUTION
If the function requires dependencies (node modules, injected Object, references out of scope, …) those will be lost and it will cause an error.

[ngnijland]

@Sean
Ah ofcourse, thanks for the explanation!

My function does not have dependencies. I’ll use good old eval to fix this!

My use case is that I need to use a different function based on the language setting of the mirror. These functions live in a separate folder and I import them in the node_helper.js file (together with some other arrays and objects I need based on language). For now I’ll use this solution, maybe in the future I build in a build step in my module so I can import the files directly into my main module file.

https://github.com/ngnijland/MMM-text-clock/pull/2