Detect if visitors are logged into Twitter, Facebook or Google+

The quick version: I’ve found a way to abuse the login mechanism for both Twitter and Google to detect whether a user is logged in to that service. Facebook provides an API for this. So I provide a cross-browser javascript template that works for all 3 networks. If you want to get straight to the code jump to the implementation section or check out the Social Network Login Status Detector Demo. In

[saladdays]

各SNSのログイン状態を調べる方法。非公式なのでいつ使えなくなるかはわからないけど、方法としてはすごいかしこい！