See if file in _includes folder exists

Can this be done? If so, how?

I tried:

```
{% iffileexists /_includes/file.js %}
  <h1>IT EXISTS</h1>
{% endiffileexists %}
```
and
```
{% iffileexists _includes/file.js %}
  <h1>IT EXISTS</h1>
{% endiffileexists %}
```
but it didn't work