pass functions to workers and and call them in subsequent messages

pass-and-call-function-in-worker.js

// 8 June 2024
// pass functions to workers and and call them in subsequent messages.

// similar to gists in 2022:
// pass functions as strings to workers and revive them with the Function() constructor 
// https://gist.github.com/dfkaye/527f163b6913b163a579bbeb01858593

// Not the same as "pass a stringified function in its own blob to a worker and
// import it using importScripts(blobUrl)."
// https://gist.github.com/dfkaye/ca9722cd247c6d907b3bbaf7273741e0

var source = `
self.onmessage = function (request) {
  var { action, value } = Object(request.data);

  if (action == 'extend') {
    extend({name, fn} = value)
  }
  else if (action in actions) {
    actions[action](...value);
  }
};
extend = function ({name, fn}) {
  actions[name] = Function("return (" + fn + ").apply(0, arguments)");

  self.postMessage({
    action: "extended",
    value: {
      name,
      fn: actions[name].toString()
    }
  });

  // console.log(actions[name])
};
actions = {}
`;
var blob = new Blob([source], {type: "text/javascript"});
var url = URL.createObjectURL(blob);
var worker = new Worker(url);

worker.onmessage = function (response) {
  var { action, value } = Object(response.data)
  console.warn("calling back:", action);
  if (action == 'extended') {
    console.warn("new function added: ", value.name, value.fn);
  }
  else {
    console.warn(action, value);
  }
};


/* test it out */


function test(a,b,c) {
  console.info("testing", a,b,c);

  self.postMessage({ action: "tested", value: a+b+c });
};

worker.postMessage({
  action: "extend",
  value: {
    name: "test",
    fn: test.toString()
  }
});

setTimeout(() => {
  worker.postMessage({
    action: "test",
    value: ["A", "B", "C"]
  });
}, 1000);

setTimeout(() => {
  worker.postMessage({
    action: "test",
    value: ["D", "E", "F"]
  });
}, 1000);

/*
calling back: extended

new function added:  test function anonymous(
) {
return (function test(a,b,c) {
  console.info("testing", a,b,c);

  self.postMessage({ action: "tested", value: a+b+c });
}).apply(0, arguments)
}

testing A B C
calling back: tested

tested ABC

testing D E F
calling back: tested

tested DEF
*/