Weevil

Like eval, but in a webworker.

npm install weevil --save

What?

Weevil makes it simple to eval JavaScript in a separate event-loop "thread" via a webworker. It also simplifies sending and receiving messages with that other thread via postmessage.

Why?

If you're kinda crazy, then you might find this handy.

Examples

Basic Usage

Pass weevil a string with javascript code in it, that'll be run in the webworker.

var weevil = require('weevil');

//This code will be run on the webworker
var workerCode = [
    "//do something slow here",
    "for (var i=0; i<1000000; i++) {",
    "  Math.pow(2,50);
    "}",
    "console.log('done');"
].join("\n");

weevil(workerCode);

we can simplify generating the code with deval, of course it still can't access any of the variables in scope of the host page, but at least it's easier to write the code.

var weevil = require('weevil');

//This code will be run on the webworker
var workerCode = deval(function () {
    //do something slow here
    for (var i=0; i<1000000; i++) {
        Math.pow(2,50);
    }
    console.log('done');
});

weevil(workerCode);

Sending messages to the worker

In the context of the webworker, there is a weevil object which effectively acts as a simple event emitter. In the context of the main thread, the worker object returned from calling weevil(theCode) has the same methods:

• weevil.emit(name, [args...]) / worker.emit(name, [args...])
  • send a message to the host page / to the worker. With name, and optional args list which the on callback will receive. Also aliased as weevil.send / worker.send.
• weevil.on(name, callback) / worker.on(name, callback)
  • listen to messages from the host page / from the worker. With name of the messages to listen for, and callback to run when the message is received. The callback will receive the list of args... from the emit call in the other process.
• weevil.once(name, callback) / worker.once(name, callback)
  • as per .on(), listen to messages from the host page / from the worker, but only run the callback only once.
• weevil.off(name, [callback]) / worker.off(name, [callback])
  • unregister listen callback(s). If a callback is specified, only that callback will be deregistered for the named event. If no callback is specified, all callbacks for message name will be deregistered.
• weevil.kill() / worker.kill()
  • Terminate the worker immediately, and deregister all handlers.

(Example: again using deval to generate the worker code string).

var deval = require('deval');
var weevil = require('weevil');

//This code will run on the webworker (note it will be run in a completely different scope
var workerCode = deval(function () {
    weevil.on('count-to', function (limit) {
        var start = new Date();
        for (var i=0; i<limit; i++) {
            Math.pow(2,50);
        }
        vae end = new Date();
        weevil.emit('count-done', end - start);
    });
});

var limit = 1000000000;
var worker = weevil(workerCode);
worker.send('count-to', limit)
      .on('count-done', function (time) {
        alert('Worker counted to ' + limit + ' in ' + time + 'ms');
      });

Who?

If you wish to heckle: Philip Roberts.

License

MIT