node-isabspath
Return true if path is an absolute pathname. On Unix, that means it begins with a slash, on Windows that it begins with a (back)slash after chopping off a potential drive letter.
Usage
var isabspath = require('isabspath')
isabspath('/root/path/to') // => true
isabspath('C:\\path\\to') // => true
isabspath('C:/path/to') // => true
isabspath('.') // => false
isabspath('./path/to') // => false