function asCallback(promise, cb, options) {
  if (typeof cb !== 'function') return promise

  let p = promise.then(function (ret) {
    if (options && options.spread && Array.isArray(ret)) {
      cb.apply(null, [null].concat(ret))
    } else cb(null, ret)
  }, cb)

  if (typeof p.done === 'function') {
    p.done()
  } else if (typeof setTimeout === 'function') {
    p.catch(asyncThrow)
  }

  return promise
}

function asyncThrow(e) {
  setTimeout(function() {throw e}, 0)
}

module.exports = asCallback

'use strict';

function asCallback(promise, cb, options) {
  if (typeof cb !== 'function') return promise

  let p = promise.then(function (ret) {
    if (options && options.spread && Array.isArray(ret)) {
      cb.apply(null, [null].concat(ret))
    } else cb(null, ret)
  }, cb)

  if (typeof p.done === 'function') {
    p.done()
  } else if (typeof setTimeout === 'function') {
    p.catch(asyncThrow)
  }

  return promise
}

function asyncThrow(e) {
  setTimeout(function() {throw e}, 0)
}

module.exports = asCallback

Fix Block-scoped declarations (let, const, function, class) not yet supported outside strict mode
Fix Block-scoped declarations (let, const, function, class) not yet supported outside strict mode

In Node v4.4.5, I get this error:

```
ascallback/index.js:4
  let p = promise.then(function (ret) {
  ^^^

SyntaxError: Block-scoped declarations (let, const, function, class) not yet supported outside strict mode
```

Using strict for this module helps.
