Lightweight promisified API wrappers

A yet another library for promisifying callback-style APIs, but this time implemented using the ES2015 Proxy object. It works by intercepting method calls to the API and returning a promise if a callback parameter was expected.

The benefit of using proxies is that the API is extended without the need to duplicate or mutate the original API implementation. The main functionality of the proxies is implemented in less than 20 lines, making this approach lightweight and easily auditable.

Used in

• promiseproxy-chrome – Promisified Chrome extension API
• promiseproxy-node – Promisified Node.js 6.x API

About Proxy

• Exploring ES6 – Metaprogramming with proxies
• You Don't Know JS – Chapter 7: Meta Programming

Requirements

Proxy requires native ES2015 support since it's not practicable to shim it for ES5 environments. It is supported in Node.js 6+, Chrome, Firefox and Edge.

• Browser support for Proxy
• Node.js support for Proxy

API

Example

const {PromiseProxy} = require("promiseproxy")

PromiseProxy(target, schema) ⇒ Proxy ⏏

Factory of Proxy objects for recursively promisifying a callback-based API

Kind: global method of promiseproxy

Param	Type	Description
target	Object	The API to be promisifed
schema	Object	API structure with callback parameter position

Example

// Define chrome.tabs.query(_, callback) and .update(_, _, callback) methods
// 1 and 2 are the positions of the callback parameters (zero-based)
const schema = {tabs: {query: 1, update: 2}}
// Promisify the Chrome API based on the schema
const _chrome = PromiseProxy(chrome, schema)
// The promisified methods return a Promise if the callback parameter is omitted
_chrome.tabs.query(info).then(callback)
// The same methods can still be used with a callback
_chrome.tabs.query(info, callback)