Data loss in Node.js child process

Question

I'm trying to send data (as an object) to a child process in Node.js, however, all of my regular expressions get lost in transfer.

var arguments = {
    something: { 
       name: 'test',       
       age: 28,
       active; true          
    },
    otherThing: 'some string',
    regex: /test/i,
    regex2: new RegExp('test')
};

var child = cp.fork(path.join(__dirname, 'child.js'));

child.on('message', function (data) {
   console.log(data);
});

child.send(arguments);

In the child.js file I have this at the top:

process.on('message', function () {
   console.log(arguments); // This is where the data has changed
});

When the log is output from the child process the arguments object instead looks like this:

{
    something: {
        name: 'test',
        age: 28,
        active: true
    },
    otherThing: 'some string',
    regex: {},
    regex2: {}
}

So far unable to find anything elsewhere about why this may be happening, any ideas?

Answer 1

Because they are completely separate JavaScript processes, you can't send objects. When you pass an object, it gets serialized to JSON and parsed by the child. (See the docs.)

JSON does not support serializing regex objects. (Try putting JSON.stringify(/abc/) through your console -- you get back "{}".)

To include regexes in a JSON object, you can use the json-fn module. It supports serializing functions, dates, and regexes. (It was actually thanks to an issue i raised that they added regex support. :))

You could then do something like:

var JSONfn = require('json-fn');
var arguments = {
    something: { 
       name: 'test',       
       age: 28,
       active; true          
    },
    otherThing: 'some string',
    regex: /test/i,
    regex2: new RegExp('test')
};

var child = cp.fork(path.join(__dirname, 'child.js'));
});

child.send(JSONfn.stringify(arguments));

and:

var JSONfn = require('json-fn');
process.on('message', function (data) {
   console.log(JSONfn.parse(data))); // This is where the data has changed
});