WebWorkerWrapper

Javascript is a single-threaded language, but it is possible to execute javascript code on a background thread using Web Workers.

These workers have limitations, the most problematic for me was the way to communicate with the main thread : only string messages can be sent between the UI and the background threads.

In order to have an easier way to communicate between threads, I made this wrapper, that will allow to directly call functions with parameters on the background threads, with a callback when the process is done.

The project contains the following files :

• js/code.js : this file contains a javascript object with the functions we want to call on background worker
• js/worker.js : the background worker itself
• js/wrapper.js : here we have the entry point for the background functions
• default.html : well, we need it to make all this work together

How to use it

If you want to use a wrapper like this one, here is what you have to know :

The heavy tasks are in an object named Code in the code.js file. Only the functions in this object will be wrapped to be used in the worker.

If you rename the file, update the first line of the worker.js.

If you rename the object Code, update the call to this object in wrapper.js and worker.js

In your html file, add a reference to code.js and wrapper.js. The worker.js is already referenced in wrapper.js (be careful to the path to the file)

All the functions in the object Code can be directly called synchronously. An object BackgroundWorker is created with the same functions, and they can receive one more parameter : a callback to call at the end.

Code sample

code.js :

var Code = {
    HeavyCalculation(param1, param2) {
        // Do all your stuff here
        return "here is the result";
    }
};

any other script :

var output = document.getElementById("output");
// Synchronous call
// If you do this, the browser will freeze 
var result = Code.HeavyCalculation(12, 456);
output.textContent = result;

// Asynchronous call
// Here the browser won't freeze : the call is made in 
// the background, at the end the result is displayed
BackgroundWorker.HeavyCalculation(12, 456, function callback(result){
    output.textContent = result;
});

Limitations

As the messaging between the threads is limited to json objects, the parameters of the functions can only be serializables javascript objects ; no functions allowed.

The background worker is still single threaded : if you call several functions, they will be queued.

Blog post

If you speak french, I explained all this code here : http://blog.lacasa.fr/2014/simplifier-worker-javascript.html