javascript - How to pass functioncallback to child process in Node.js? - Stack Overflow

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Let's say I have a parent.js containing a method named parent

var childProcess = require('child_process');

var options = {
    someData: {a:1, b:2, c:3},
    asyncFn: function (data, callback) { /*do other async stuff here*/ }
};

function Parent(options, callback) {
    var child = childProcess.fork('./child');
    child.send({
        method: method,
        options: options
    });
    child.on('message', function(data){
        callback(data,err, data,result);
        child.kill();
    });
}

Meanwhile in child.js

process.on('message', function(data){
    var method = data.method;
    var options = data.options;
    var someData = options.someData;
    var asyncFn = options.asyncFn; // asyncFn is undefined at here
    asyncFn(someData, function(err, result){
        process.send({
            err: err,
            result: result
        });
    });
});

I was wondering if passing functions to child process is not allowed in Node.js.

Why would asyncFn bee undefined after it is sent to the child?

Is it related to JSON.stringify?

Let's say I have a parent.js containing a method named parent

var childProcess = require('child_process');

var options = {
    someData: {a:1, b:2, c:3},
    asyncFn: function (data, callback) { /*do other async stuff here*/ }
};

function Parent(options, callback) {
    var child = childProcess.fork('./child');
    child.send({
        method: method,
        options: options
    });
    child.on('message', function(data){
        callback(data,err, data,result);
        child.kill();
    });
}

Meanwhile in child.js

process.on('message', function(data){
    var method = data.method;
    var options = data.options;
    var someData = options.someData;
    var asyncFn = options.asyncFn; // asyncFn is undefined at here
    asyncFn(someData, function(err, result){
        process.send({
            err: err,
            result: result
        });
    });
});

I was wondering if passing functions to child process is not allowed in Node.js.

Why would asyncFn bee undefined after it is sent to the child?

Is it related to JSON.stringify?

• javascript
• node.js
• child-process

Share Improve this question Follow asked Jan 20, 2015 at 4:11 kitkit 32533 silver badges1313 bronze badges

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1 Answer 1

Sorted by: Reset to default 11

JSON doesn't support serializing functions (at least out of the box). You could convert the function to its string representation first (via asyncFn.toString()) and then re-create the function again in the child process. The problem though is you lose scope and context with this process, so your function really has to be standalone.

Complete example:

parent.js:

var childProcess = require('child_process');

var options = {
  someData: {a:1, b:2, c:3},
  asyncFn: function (data, callback) { /*do other async stuff here*/ }
};
options.asyncFn = options.asyncFn.toString();

function Parent(options, callback) {
  var child = childProcess.fork('./child');
  child.send({
    method: method,
    options: options
  });
  child.on('message', function(data){
    callback(data,err, data,result);
    child.kill();
  });
}

child.js:

process.on('message', function(data){
  var method = data.method;
  var options = data.options;
  var someData = options.someData;
  var asyncFn = new Function('return ' + options.asyncFn)();
  asyncFn(someData, function(err, result){
    process.send({
      err: err,
      result: result
    });
  });
});

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