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var Promise = require('any-promise')
var assert = require('assert')
module.exports = thenify
/**
* Turn async functions into promises
*
* @param {Function} fn
* @return {Function}
* @api public
*/
function thenify(fn, options) {
assert(typeof fn === 'function')
return createWrapper(fn, options)
}
/**
* Turn async functions into promises and backward compatible with callback
*
* @param {Function} fn
* @return {Function}
* @api public
*/
thenify.withCallback = function (fn, options) {
assert(typeof fn === 'function')
options = options || {}
options.withCallback = true
return createWrapper(fn, options)
}
function createCallback(resolve, reject, multiArgs) {
// default to true
if (multiArgs === undefined) multiArgs = true
return function(err, value) {
if (err) return reject(err)
var length = arguments.length
if (length <= 2 || !multiArgs) return resolve(value)
if (Array.isArray(multiArgs)) {
var values = {}
for (var i = 1; i < length; i++) values[multiArgs[i - 1]] = arguments[i]
return resolve(values)
}
var values = new Array(length - 1)
for (var i = 1; i < length; ++i) values[i - 1] = arguments[i]
resolve(values)
}
}
function createWrapper(fn, options) {
options = options || {}
var name = fn.name;
name = (name || '').replace(/\s|bound(?!$)/g, '')
var newFn = function () {
var self = this
var len = arguments.length
if (options.withCallback) {
var lastType = typeof arguments[len - 1]
if (lastType === 'function') return fn.apply(self, arguments)
}
var args = new Array(len + 1)
for (var i = 0; i < len; ++i) args[i] = arguments[i]
var lastIndex = i
return new Promise(function (resolve, reject) {
args[lastIndex] = createCallback(resolve, reject, options.multiArgs)
fn.apply(self, args)
})
}
Object.defineProperty(newFn, 'name', { value: name })
return newFn
}
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