mw-wrapper.js

function wrap( middleware, trigger ){
  return function( req, res, next ){
    // The trigger can be a function that gets dynamically evaluated every time
    // or a static truthy/falsy variable
    if( typeof trigger === 'function' ? trigger() : trigger ){
      middleware( req, res, next )
    }
    else{
      next();
    }
  }
}