# findIndex

Searches for an element that matches the conditions defined by the specified predicate, and returns the first occurrence within the entire Observable sequence.

## Arguments

1. `predicate` _(`Function`)_: A function to test each source element for a condition;  The callback is called with the following information:
   1. the value of the element
   2. the index of the element
   3. the Observable object being subscribed
2. `[thisArg]` _(`Any`)_: Object to use as `this` when executing the predicate.

## Returns

_(`Observable`)_: An Observable sequence with the first element that matches the conditions defined by the specified predicate, if found; otherwise, undefined.

## Example

```javascript
/* Not found */
var array = [1,2,3,4];

var source = Rx.Observable.from(array)
  .findIndex(function (x, i, obs) { return x === 5; });

var subscription = source.subscribe(
  function (x) {
    console.log('Next: %s', x);
  },
  function (err) {
    console.log('Error: %s', err);
  },
  function () {
    console.log('Completed');
  });

// => Next: -1
// => Completed
```
