Social Sharing Buttons Under Control: Socialite.js
The library is lightweight (2kb minified-gzipped), standalone and helps the social widgets to load when you want them or only when needed/requested to speed up web pages.
It has support for the major players: Twitter, Google+, Facebook, LinkedIn, Pinterest, and Spotify. There is no need to install the widget codes for each library as Socialite.js does that for you.
And, the library is extensible, any new social networks can be added with ease.