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const promiseToCallback = require('promise-to-callback')
const callbackNoop = function (err) { if (err) throw err }
/**
* A generator that returns a function which, when passed a promise, can treat that promise as a node style callback.
* The prime advantage being that callbacks are better for error handling.
*
* @param {Function} fn The function to handle as a callback
* @param {Object} context The context in which the fn is to be called, most often a this reference
*
*/
module.exports = function nodeify (fn, context) {
return function () {
// parse arguments
const args = [].slice.call(arguments)
const lastArg = args[args.length - 1]
const lastArgIsCallback = typeof lastArg === 'function'
let callback
if (lastArgIsCallback) {
callback = lastArg
args.pop()
} else {
callback = callbackNoop
}
// call the provided function and ensure result is a promise
let result
try {
result = Promise.resolve(fn.apply(context, args))
} catch (err) {
result = Promise.reject(err)
}
// wire up promise resolution to callback
promiseToCallback(result)(callback)
}
}
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