path.normalize(p)

path.normalize('/foo/bar//baz/asdf/quux/..')
// returns
'/foo/bar/baz/asdf'

// windows version
  exports.normalize = function(path) {
    var result = splitDeviceRe.exec(path),
        device = result[1] || '',
        isUnc = device && device.charAt(1) !== ':',
        isAbsolute = exports.isAbsolute(path),
        tail = result[3],
        trailingSlash = /[////]$/.test(tail);
 
    // If device is a drive letter, we'll normalize to lower case.
    if (device && device.charAt(1) === ':') {
      device = device[0].toLowerCase() + device.substr(1);
    }
 
    // Normalize the tail path
    tail = normalizeArray(tail.split(/[////]+/).filter(function(p) {
      return !!p;
    }), !isAbsolute).join('//');
 
    if (!tail && !isAbsolute) {
      tail = '.';
    }
    if (tail && trailingSlash) {
      tail += '//';
    }
 
    // Convert slashes to backslashes when `device` points to an UNC root.
    // Also squash multiple slashes into a single one where appropriate.
    if (isUnc) {
      device = normalizeUNCRoot(device);
    }
 
    return device + (isAbsolute ? '//' : '') + tail;
  };