what does it mean ~ operator in javaScript

Question

i have no idea of the meaning the operator ~ in javascript, for example, look the next code:

function canonicalizeResource (resource) {
  var url = parse(resource, true)
    , path = url.pathname
    , buf = []
    ;

  Object.keys(url.query).forEach(function(key){
    if (!~keys.indexOf(key)) return
    var val = '' == url.query[key] ? '' : '=' + encodeURIComponent(url.query[key])
    buf.push(key + val)
  })

  return path + (buf.length ? '?' + buf.sort().join('&') : '')
}