webworker-threads/examples/ex02_events.md

Lightweight Web Worker API implementation with native threads

## Sending events from a worker thread

This second example demonstrates how we can use events to communicate from the worker
thread to the main thread.

Like before, we create a thread and we define the fibonacci function:

``` javascript
var Threads = require('webworker-threads');
var t = Threads.create();

function fibo(n) {
	return n > 1 ? fibo(n - 1) + fibo(n - 2) : 1;
}
```

Instead of running a single fibonacci computation in the worker thread, we are going to execute a function
that computes all fibonacci numbers and emits a `data` event for every number it generates.

This function runs inside the worker thread so it does not see the `t` variable which belongs to the 
main thread. But **webworker-threads** sets up a global `thread` variable that the worker thread can use to 
send events to the main thread.

Here is our fibonacci generator:

``` javascript
function generateFibos(max) {
	for (var i = 1; i <= max; i++) {
		thread.emit("data", i, fibo(i));
	}
}
```

Note: this is obviously a very inefficient algorithm to generate the sequence of fibonacci numbers.

Inside the main thread, we set up an event listener for the `data` events emitted by the 
worker thread:

``` javascript
t.on('data', function(n, result) {
	console.log('fibo(' + n + ') = ' + result);
})
```

Now, we are ready to go. We load the two functions into the worker thread

``` javascript
t.eval(fibo);
t.eval(generateFibos);
```

And we run the generator with a callback that will execute when the generator returns from its loop:

``` javascript
t.eval("generateFibos(40)", function(err, result) {
	if (err) throw err;
	console.log("generator is done!");
	t.destroy();
});
```

### Output

```
fibo(1) = 1
fibo(2) = 2
fibo(3) = 3
fibo(4) = 5
...
fibo(39) = 102334155
fibo(40) = 165580141
generator is done!
```