# <a id="promise"></a>promise

Helpers for bridging the gap between nodejs APIs and promises.

## Contents

**Module Members**

- [wrap()](#wrap)
- [once()](#once)

## Module Members

#### <a id="wrap"></a>wrap( fn )

Wrap the given synchronous function so that it always returns a promise.

##### Parameters

| Property | Type | Description |
| -------- | ---- | ----------- |
| fn | `Function` |  the function to wrap |

##### Returns

| Type | Description |
| ---- | ----------- |
| `Function` |  a function that returns a promise resolving to the value returned by `fn` or being rejected in case the wrapped function throws an exception |

#### <a id="once"></a>once( fn, values, map )

Wrap the given function so that it is only called once for equal parameters.
Subsequent calls with the same first argument will return either the same promise, or a promise which
resolves to a value that is modified by the given map function.

##### Parameters

| Property | Type | Description |
| -------- | ---- | ----------- |
| fn | `Function` |  the function to wrap |
| _values_ | `Object` |  a pre-filled map, mapping arguments to promises that should be returned |
| _map_ | `Function` |  a function that is used to determine the return value of subsequent calls |

##### Returns

| Type | Description |
| ---- | ----------- |
| `Function` |  a function that returns a promise resolving to the value returned by `fn` or, for subsequent calls with the same argument, the value returned by `map` |