@function can-zone.waitFor waitFor
@parent can-zone.static

@signature `Zone.waitFor(fn)`

**Zone.waitFor** is a function that creates a callback that can be used with any async functionality. Calling Zone.waitFor registers a wait with the currently running request and returns a function that, when called, will decrement the wait count.

This is useful if there is async functionality other than what [we implement](#tasks). You might be using a library that has C++ bindings and doesn't go through the normal JavaScript async APIs.

```js
import Zone from "can-zone";
import fs from "fs";

fs.readFile( "data.json", "utf8", Zone.waitFor( function() {

	// We waited on this!
} ) );
```

@param {function} fn