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## Running a simple function in a thread
This first example demonstrates how you can run an expensive computation in
a worker thread and obtain its result.
First, we define the function that we want to execute in the worker thread:
``` javascript
function fibo(n) {
return n > 1 ? fibo(n - 1) + fibo(n - 2) : 1;
}
```
Then, we create a worker thread with the `Threads.create` call:
``` javascript
var Threads = require('webworker-threads');
var t = Threads.create();
```
In the next step, we load the function into the worker thead.
We get the function's source with `fibo.toString()` and we
call `t.eval(source)` to evalutate it into the worker thread's context:
``` javascript
t.eval(fibo);
```
Now, we are ready to call this function.
We use the `t.eval` function again, with two arguments this time.
The first argument is the expression to evaluate.
The second one is a callback that receives the result (or an error if there was one).
``` javascript
t.eval('fibo(10)', function(err, result) {
if (err) throw err; // something abnormal
// print the result
console.log('fibo(10)=' + result);
// chain with next step
step2();
});
```
Let's call it again:
``` javascript
function step2() {
t.eval('fibo(20)', function(err, result) {
if (err) throw err;
console.log('fibo(20)=' + result);
step3();
});
}
```
If the expression is invalid, we get an error through the callback
``` javascript
function step3() {
// 'x' is not defined
t.eval('fibo(x)', function(err, result) {
console.log('error=' + err);
step4();
});
}
```
But the thread is still alive and ready to accept more calls:
``` javascript
function step4() {
t.eval('fibo(15)', function(err, result) {
console.log('fibo(15)=' + result);
step5();
});
}
```
Once we are done, we destroy the thread:
``` javascript
function step5() {
t.destroy();
}
```
### Output
```
fibo(10)=89
fibo(20)=10946
error=Error: ReferenceError: x is not defined
fibo(15)=987
```
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